Add zizmor workflow to audit GitHub Actions workflows

Runs zizmor on changes to .github/** to catch common security issues
in CI workflows such as unpinned actions and injection risks.

Signed-off-by: Dan Childers <dchilder@redhat.com>

Author: danchild

.github/workflows/zizmor.yml

@@ -0,0 +1,28 @@
+name: zizmor
+
+on:
+  push:
+    branches:
+      - main
+    paths:
+      - '.github/**'
+  pull_request:
+    paths:
+      - '.github/**'
+
+permissions: {}
+
+jobs:
+  zizmor:
+    runs-on: ubuntu-latest
+    permissions:
+      security-events: write
+      contents: read
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          persist-credentials: false
+
+      - name: Run zizmor
+        uses: zizmorcore/zizmor-action@192e21d79ab29983730a13d1382995c2307fbcaa # v0.5.7