CI: use BuildJet & large Windows runners

1. Use buildjet for the longer Linux CI workflows.
2. Continue with `ubuntu-latest` for shorter Linux CI workflows.
3. Use a large GitHub-hosted Windows runner.
   https://docs.github.com/en/actions/using-github-hosted-runners/using-larger-runners
4. Make CIFuzz run on merge to main or release branch, not
   in the pull request

Two runs each of the original workflow files and the updated
workflows in this PR. One run of the GitHub Large Ubuntu runners
is included; these are clearly between the regular GitHub and BuildJet
runners in performance.
                              GitHub  GitHub  BuildJet BuildJet  GHLarge
codeql-analysis.yml           4m 30s  cached   2m 56s   2m 59s   4m  0s
cross-darwin.yml              3m 10s  3m 19s   1m 33s   1m 30s   2m 43s
cross-freebsd.yml             3m 33s  3m 10s   1m 28s   1m 22s   2m 15s
cross-openbsd.yml             3m  4s  2m 36s   1m 29s   1m 22s   2m  3s
cross-wasm.yml                1m 59s  2m  2s   1m 12s   1m 16s   1m 46s
cross-windows.yml             2m 45s  3m  0s   1m 44s   1m 25s   2m  6s
linux32.yml                   4m 27s  4m  0s   1m 55s   2m  8s   2m 51s
linux-race.yml                3m 54s  4m  7s   2m 22s   2m 12s   3m 14s
linux.yml                     4m 23s  4m 39s   2m 37s   2m 15s   3m 38s
static-analysis.yml
 /vet                         1m 41s  2m 22s      52s      56s   1m 12s
 /staticcheck(linux, amd64)   2m 47s  2m 38s   1m  7s   1m 10s   1m 52s
 /staticcheck(windows, amd64) 2m  5s  2m  4s   1m  6s   1m  8s   1m 33s
 /staticcheck(darwin, amd64)  2m 14s  2m 20s   1m 10s   1m 10s   1m 50s
 /staticcheck(windows, 386)   2m 36s  1m 58s   1m 23s   1m  8s   1m 39s
vm.yml                        1m 30s  1m 32s   2m 31s   2m 23s   N/A

A few very short workflows are being left on GitHub-hosted runners, like
licenses and gofmt. These benefit from the quicker dispatch to GitHub
hosted runners.

--------

For Windows and the windows.yml test run:
- the regular `windows-latest` runner takes about 6 minutes 20 seconds
- there is enough variability run to run that we get the same ~4 minute
  run with:
    - a GitHub-hosted large runner
    - a self-hosted Windows Server 2022 in an AWS t3.xlarge
    - a self-hosted Windows Server 2022 in an AWS c6i.xlarge
Since there is not a gain from operating our own runner, we'll pay
GitHub to operate a Windows large runner.

Signed-off-by: Denton Gentry <dgentry@tailscale.com>

.github/workflows/cifuzz.yml

@@ -1,5 +1,7 @@
 name: CIFuzz
-on: [pull_request]
+on:
+  push:
+    branches: [ main, release-branch/* ]
 
 concurrency:
   group: ${{ github.workflow }}-$${{ github.head_ref || github.run_id }}
@@ -7,7 +9,7 @@ concurrency:
 
 jobs:
   Fuzzing:
-    runs-on: ubuntu-latest
+    runs-on: buildjet-4vcpu-ubuntu-2204
     steps:
     - name: Build Fuzzers
       id: build
@@ -20,7 +22,7 @@ jobs:
       uses: google/oss-fuzz/infra/cifuzz/actions/run_fuzzers@master
       with:
         oss-fuzz-project-name: 'tailscale'
-        fuzz-seconds: 300
+        fuzz-seconds: 900
         dry-run: false
         language: go
     - name: Upload Crash

.github/workflows/codeql-analysis.yml

@@ -27,7 +27,7 @@ concurrency:
 jobs:
   analyze:
     name: Analyze
-    runs-on: ubuntu-latest
+    runs-on: buildjet-4vcpu-ubuntu-2204
     permissions:
       actions: read
       contents: read

.github/workflows/cross-android.yml

@@ -14,7 +14,7 @@ concurrency:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: buildjet-4vcpu-ubuntu-2204
 
     if: "!contains(github.event.head_commit.message, '[ci skip]')"
 

.github/workflows/cross-darwin.yml

@@ -14,7 +14,7 @@ concurrency:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: buildjet-4vcpu-ubuntu-2204
 
     if: "!contains(github.event.head_commit.message, '[ci skip]')"
 

.github/workflows/cross-freebsd.yml

@@ -14,7 +14,7 @@ concurrency:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: buildjet-4vcpu-ubuntu-2204
 
     if: "!contains(github.event.head_commit.message, '[ci skip]')"
 

.github/workflows/cross-openbsd.yml

@@ -14,7 +14,7 @@ concurrency:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: buildjet-4vcpu-ubuntu-2204
 
     if: "!contains(github.event.head_commit.message, '[ci skip]')"
 

.github/workflows/cross-wasm.yml

@@ -14,7 +14,7 @@ concurrency:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: buildjet-4vcpu-ubuntu-2204
 
     if: "!contains(github.event.head_commit.message, '[ci skip]')"
 

.github/workflows/cross-windows.yml

@@ -14,7 +14,7 @@ concurrency:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: buildjet-4vcpu-ubuntu-2204
 
     if: "!contains(github.event.head_commit.message, '[ci skip]')"
 

.github/workflows/linux-race.yml

@@ -14,7 +14,7 @@ concurrency:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: buildjet-4vcpu-ubuntu-2204
 
     if: "!contains(github.event.head_commit.message, '[ci skip]')"
 

.github/workflows/linux.yml

@@ -14,7 +14,7 @@ concurrency:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: buildjet-4vcpu-ubuntu-2204
 
     if: "!contains(github.event.head_commit.message, '[ci skip]')"
 
@@ -38,10 +38,6 @@ jobs:
 
     - name: Get QEMU
       run: |
-        # The qemu in Ubuntu 20.04 (Focal) is too old; we need 5.x something
-        # to run Go binaries. 5.2.0 (Debian bullseye) empirically works, and
-        # use this PPA which brings in a modern qemu.
-        sudo add-apt-repository -y ppa:jacob/virtualisation
         sudo apt-get -y update
         sudo apt-get -y install qemu-user
 

.github/workflows/linux32.yml

@@ -14,7 +14,7 @@ concurrency:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: buildjet-4vcpu-ubuntu-2204
 
     if: "!contains(github.event.head_commit.message, '[ci skip]')"
 

.github/workflows/static-analysis.yml

@@ -40,7 +40,7 @@ jobs:
       if: failure() && github.event_name == 'push'
 
   vet:
-    runs-on: ubuntu-latest
+    runs-on: buildjet-4vcpu-ubuntu-2204
     steps:
     - name: Set up Go
       uses: actions/setup-go@v3
@@ -66,7 +66,7 @@ jobs:
       if: failure() && github.event_name == 'push'
 
   staticcheck:
-    runs-on: ubuntu-latest
+    runs-on: buildjet-4vcpu-ubuntu-2204
     strategy:
       matrix:
         goos: [linux, windows, darwin]

.github/workflows/vm.yml

@@ -11,7 +11,7 @@ concurrency:
 
 jobs:
   ubuntu2004-LTS-cloud-base:
-    runs-on: [ self-hosted, linux, vm ]
+    runs-on: buildjet-4vcpu-ubuntu-2204
 
     if: "!contains(github.event.head_commit.message, '[ci skip]')"
 
@@ -27,12 +27,17 @@ jobs:
         with:
           go-version-file: go.mod
 
+      - name: Get QEMU
+        run: |
+          sudo apt-get -y update
+          sudo apt-get -y install qemu-system-x86 qemu-user genisoimage qemu-utils
+
       - name: Run VM tests
         run: go test ./tstest/integration/vms -v -no-s3 -run-vm-tests -run=TestRunUbuntu2004
         env:
           HOME: "/tmp"
           TMPDIR: "/tmp"
-          XDG_CACHE_HOME: "/var/lib/ghrunner/cache"
+          XDG_CACHE_HOME: "/home/runner/cache"
 
       - uses: k0kubun/action-slack@v2.0.0
         with:

.github/workflows/windows.yml

@@ -14,7 +14,7 @@ concurrency:
 
 jobs:
   test:
-    runs-on: windows-latest
+    runs-on: windows-8vcpu
 
     if: "!contains(github.event.head_commit.message, '[ci skip]')"