github/workflows: move race tests to their own job

They're slow. Make them their own job that can run in parallel.

Also, only run them in race mode. No need to run them on 386
or non-race amd64.

Updates #7894

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

.github/workflows/test.yml

@@ -39,6 +39,16 @@ concurrency:
   cancel-in-progress: true
 
 jobs:
+  race-root-integration:
+    runs-on: ubuntu-22.04
+    steps:
+    - name: checkout
+      uses: actions/checkout@v4
+    - name: build test wrapper
+      run: ./tool/go build -o /tmp/testwrapper ./cmd/testwrapper
+    - name: integration tests as root
+      run: PATH=$PWD/tool:$PATH /tmp/testwrapper --sudo ./tstest/integration/ -race
+
   test:
     strategy:
       fail-fast: false # don't abort the entire matrix if one element fails
@@ -90,8 +100,6 @@ jobs:
         sudo apt-get -y install qemu-user
     - name: build test wrapper
       run: ./tool/go build -o /tmp/testwrapper ./cmd/testwrapper
-    - name: integration tests as root
-      run: PATH=$PWD/tool:$PATH /tmp/testwrapper --sudo ./tstest/integration/ ${{matrix.buildflags}}
     - name: test all
       run: PATH=$PWD/tool:$PATH /tmp/testwrapper ./... ${{matrix.buildflags}}
       env: