various: add golangci-lint, fix issues (#7905)

This adds an initial and intentionally minimal configuration for
golang-ci, fixes the issues reported, and adds a GitHub Action to check
new pull requests against this linter configuration.

Signed-off-by: Andrew Dunham <andrew@du.nham.ca>
Change-Id: I8f38fbc315836a19a094d0d3e986758b9313f163

.github/workflows/golangci-lint.yml

@@ -0,0 +1,40 @@
+name: golangci-lint
+on:
+  # For now, only lint pull requests, not the main branches.
+  pull_request:
+
+  # TODO(andrew): enable for main branch after an initial waiting period.
+  #push:
+  #  branches:
+  #    - main
+
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  pull-requests: read
+
+concurrency:
+  group: ${{ github.workflow }}-$${{ github.head_ref || github.run_id }}
+  cancel-in-progress: true
+
+jobs:
+  golangci:
+    name: lint
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+
+      - uses: actions/setup-go@v3
+        with:
+          go-version-file: go.mod
+          cache: false
+
+      - name: golangci-lint
+        # Note: this is the 'v3' tag as of 2023-04-17
+        uses: golangci/golangci-lint-action@08e2f20817b15149a52b5b3ebe7de50aff2ba8c5
+        with:
+          version: v1.52.2
+
+          # Show only new issues if it's a pull request.
+          only-new-issues: true