spike: add workflow to build multi-arch test image

.github/workflows/tag_test.yaml

@@ -0,0 +1,44 @@
+name: Publish Test Docker image
+
+on:
+  push:
+    tags:
+      - '**'
+
+jobs:
+  push_to_registry:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Extract Tags
+        id: tags
+        run: |
+          IMAGE_VERSION="${GITHUB_REF/refs\/tags\//}"
+          TAGS="ghcr.io/inshur/fy-test:$IMAGE_VERSION"
+          echo "IMAGE_VERSION=${IMAGE_VERSION}" >> "$GITHUB_ENV"
+          echo "TAGS=${TAGS}" >> "$GITHUB_ENV"
+          echo "$TAGS"
+          echo "tags=${TAGS}" >> "$GITHUB_OUTPUT"
+
+      - name: Check out repo
+        uses: actions/[email protected]
+
+      - uses: docker/setup-buildx-action@v3
+
+      - name: Login to GitHub Container Registry
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.repository_owner }}
+          password: ${{ secrets.GHCR_PAT }}
+
+      - name: Push to GitHub Packages
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          push: true
+          platforms: linux/amd64,linux/arm64
+          # failing to use a variable here for some reason:
+          # Error: buildx call failed with: invalid tag "${TAGS}": invalid reference format
+          #tags: inshur/fy:latest
+          tags: ${{ steps.tags.outputs.tags }}
+