gha: add golangci-lint

Linting is disabled on Windows, as the current build-tags do not
properly exclude non-unix platforms;

    level=info msg="[runner/filename_unadjuster] Pre-built 0 adjustments in 1.0348ms"
    Error: level=error msg="[linters_context] typechecking error: D:\\a\\netns\\netns\\netns.go:28:18: Stat_t not declared by package unix"
    Error: level=error msg="[linters_context] typechecking error: D:\\a\\netns\\netns\\netns.go:29:17: Fstat not declared by package unix"
    Error: level=error msg="[linters_context] typechecking error: D:\\a\\netns\\netns\\netns.go:32:17: Fstat not declared by package unix"
    Error: level=error msg="[linters_context] typechecking error: D:\\a\\netns\\netns\\netns.go:43:13: Stat_t not declared by package unix"
    Error: level=error msg="[linters_context] typechecking error: D:\\a\\netns\\netns\\netns.go:44:17: Fstat not declared by package unix"
    Error: level=error msg="[linters_context] typechecking error: D:\\a\\netns\\netns\\netns.go:56:13: Stat_t not declared by package unix"
    Error: level=error msg="[linters_context] typechecking error: D:\\a\\netns\\netns\\netns.go:57:17: Fstat not declared by package unix"
    Error: level=error msg="[linters_context] typechecking error: D:\\a\\netns\\netns\\netns.go:71:17: Close not declared by package unix"

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

.github/workflows/validate.yml

@@ -0,0 +1,49 @@
+name: validate
+on:
+  push:
+    tags:
+      - v*
+    branches:
+      - master
+      - main
+  pull_request:
+    branches:
+      - master
+      - main
+
+jobs:
+  linters:
+    permissions:
+      contents: read      # for actions/checkout to fetch code
+      pull-requests: read # for golangci/golangci-lint-action to fetch pull requests
+    timeout-minutes: 10
+
+    strategy:
+      matrix:
+        # We only run on the latest version of go, as some linters may be
+        # version-dependent (for example gofmt can change between releases).
+        go-version: [stable]
+        os: [ubuntu-22.04, windows-2022]
+    runs-on: ${{ matrix.os }}
+    steps:
+      - name: Install Go
+        uses: actions/setup-go@v3
+        with:
+          go-version: ${{ matrix.go-version }}
+      - name: Checkout code
+        uses: actions/checkout@v3
+      - name: Lint
+        uses: golangci/golangci-lint-action@v3
+        with:
+          version: latest
+          skip-cache: true
+          args: --print-resources-usage --verbose
+
+          # Optional: show only new issues if it's a pull request. The default value is `false`.
+          # only-new-issues: true
+
+          # Optional: if set to true then the action don't cache or restore ~/go/pkg.
+          # skip-pkg-cache: true
+
+          # Optional: if set to true then the action don't cache or restore ~/.cache/go-build.
+          # skip-build-cache: true

.golangci.yml

@@ -0,0 +1,2 @@
+run:
+  timeout: 5m