Update IMAGE_PUSH condition in test_docker.yml

Signed-off-by: varg1714 <51254954+varg1714@users.noreply.github.com>

Author: varg1714

.github/workflows/test_docker.yml

@@ -21,7 +21,7 @@ env:
   REGISTRY: ghcr.io
   ARTIFACT_NAME: 'binaries_docker_release'
   RELEASE_PLATFORMS: 'linux/amd64,linux/arm64,linux/arm/v7,linux/386,linux/arm/v6,linux/ppc64le,linux/riscv64,linux/loong64' ### Temporarily disable Docker builds for linux/s390x architectures for unknown reasons.
-  IMAGE_PUSH: ${{ github.event_name == 'push' }}
+  IMAGE_PUSH: ${{ github.event_name == 'push' || vars.IMAGE_PUSH || false }}
   IMAGE_TAGS_BETA: |
     type=ref,event=pr
     type=raw,value=beta,enable={{is_default_branch}}