fix: add missing 'login to Docker Hub' step to multi-arch build job

.github/workflows/continuous_integration.yml

@@ -60,6 +60,11 @@ jobs:
         uses: docker/setup-buildx-action@v3
       - name: Checkout source code
         uses: actions/checkout@v4
+      - name: Log in to Docker Hub Container Registry
+        uses: docker/login-action@v3
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
       - name: Build and push Docker image for main branch
         run: |
           make release GOTENBERG_VERSION=edge