ci: Keep Trivy cache up-to-date on default branch

See https://github.com/aquasecurity/trivy-action?tab=readme-ov-file#updating-caches-in-the-default-branch

.github/workflows/update-trivy-cache.yml

@@ -0,0 +1,43 @@
+name: Update Trivy cache
+
+on:
+  schedule:
+    - cron: '0 5 * * *'  # Night in America/Los_Angeles, before deploy-nightly.
+  workflow_dispatch:
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  update-trivy-cache:
+    runs-on: ubuntu-latest
+    env:
+      TRIVY_CACHE_PATH: .cache/trivy
+    steps:
+      - uses: oras-project/setup-oras@v1
+
+      - name: Get current date
+        id: get-date
+        run: echo "date=$(date +'%Y-%m-%d')" >> "$GITHUB_OUTPUT"
+
+      - name: Download vulnerability DB
+        run: oras pull ghcr.io/aquasecurity/trivy-db:2
+
+      - name: Download Java DB
+        run: oras pull ghcr.io/aquasecurity/trivy-java-db:1
+
+      - name: Extract vulnerability DB
+        run: |
+          mkdir -p "$TRIVY_CACHE_PATH/db"
+          tar -xf db.tar.gz -C "$TRIVY_CACHE_PATH/db"
+
+      - name: Extract Java DB
+        run: |
+          mkdir -p "$TRIVY_CACHE_PATH/java-db"
+          tar -xf javadb.tar.gz -C "$TRIVY_CACHE_PATH/java-db"
+
+      - name: Save cache
+        uses: actions/cache/save@v4
+        with:
+          path: ${{ env.TRIVY_CACHE_PATH }}
+          key: cache-trivy-${{ steps.get-date.outputs.date }}