ci: Add golangci linter

Use machines to do (at least some) of the work humans had to do!

https://github.com/containers/toolbox/pull/974

.github/workflows/linting.yaml

@@ -0,0 +1,25 @@
+name: Golangci Lint
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+
+permissions:
+  contents: read
+  pull-requests: read
+
+jobs:
+  golangci:
+    name: Lint
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: golangci-lint
+        uses: golangci/golangci-lint-action@v2
+        with:
+          version: latest
+          working-directory: ./src
+          only-new-issues: true