chore(ci): upgrade docker actions to fix Node.js 20 deprecation

- docker/login-action v3 → v4
- docker/build-push-action v6 → v7

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.github/workflows/build-test-container.yml

@@ -27,14 +27,14 @@ jobs:
         run: echo "name=${IMAGE,,}" >> "$GITHUB_OUTPUT"
 
       - name: Log in to GHCR
-        uses: docker/login-action@v3
+        uses: docker/login-action@v4
         with:
           registry: ghcr.io
           username: ${{ github.actor }}
           password: ${{ secrets.GITHUB_TOKEN }}
 
       - name: Build and push
-        uses: docker/build-push-action@v6
+        uses: docker/build-push-action@v7
         with:
           context: tests/infrastructure
           file: tests/infrastructure/Dockerfile