test: add temporary workflow to test docker-manifest action

Author: mchmarny

.github/workflows/test-manifest.yaml

@@ -0,0 +1,34 @@
+# Temporary workflow to test docker-manifest action using existing v0.5.11 images.
+# Delete after manifest creation is confirmed working.
+
+name: Test Docker Manifest
+
+on:
+  workflow_dispatch: {}
+
+permissions:
+  contents: read
+
+env:
+  VALIDATOR_IMAGE: ghcr.io/nvidia/eidos-validator
+
+jobs:
+  test-manifest:
+    name: Test Manifest Creation
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    permissions:
+      contents: read
+      packages: write
+    steps:
+      - name: Checkout Code
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd  # v6.0.2
+
+      - name: Authenticate to registry
+        uses: ./.github/actions/ghcr-login
+
+      - name: Create multi-arch manifest
+        uses: ./.github/actions/docker-manifest
+        with:
+          image: ${{ env.VALIDATOR_IMAGE }}
+          tag: v0.5.11