golangci-lint: run in own GitHub Actions job

By using the golangci-lint action after other go commands, conflicting
files during the "prepare environment" phase occurred. This known
issue[0] is easily fixable by putting golangci-lint in its own job.

[0] golangci/golangci-lint-action#23

.github/workflows/go.yml

@@ -21,6 +21,12 @@ jobs:
       run: go test -v ./...
     - name: Vet
       run: go vet ./...
+
+  golangci-lint:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - uses: actions/setup-go@v4
     - name: golangci-lint
       uses: golangci/golangci-lint-action@v3
       with: