Add weekly cargo-audit CI run

Author: bjorn3

.github/workflows/audit.yml

@@ -0,0 +1,16 @@
+name: Security audit
+on:
+  workflow_dispatch:
+  schedule:
+    - cron: '0 10 * * 1' # every monday at 10:00 UTC
+permissions:
+  issues: write
+  checks: write
+jobs:
+  audit:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: rustsec/audit-check@v1.4.1
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}