ci: add GitHub Action linter

Signed-off-by: Nathan Weinberg <nweinber@redhat.com>

.github/actions/actionlint.yml

@@ -0,0 +1,24 @@
+name: Lint GitHub Actions workflows
+on:
+  push:
+    branches: ["main"]
+    paths:
+      - '.github/**'
+  pull_request:
+    branches: ["main"]
+    paths:
+      # This regex should match the one used for mergify policy in .github/mergify.yml
+      - '.github/**'
+
+jobs:
+  actionlint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Download actionlint
+        id: get_actionlint
+        run: bash <(curl https://raw.githubusercontent.com/rhysd/actionlint/main/scripts/download-actionlint.bash)
+        shell: bash
+      - name: Check workflow files
+        run: PATH=".:$PATH" make action-lint
+        shell: bash