Do not push gcc image unless we are on main branch

Author: Bronek

.github/workflows/gcc.yml

@@ -87,7 +87,7 @@ jobs:
           context: .
           file: docker/gcc/Dockerfile.${{ matrix.os.compiler_version }}-${{ matrix.os.release }}
           labels: ${{ steps.meta.outputs.labels }}
-          outputs: type=image,name=${{ env.CONTAINER_IMAGE }},push-by-digest=true,name-canonical=true,push=true
+          outputs: type=image,name=${{ env.CONTAINER_IMAGE }},push-by-digest=true,name-canonical=true,push=${{ github.ref_type == 'branch' && github.ref_name == github.event.repository.default_branch }}
           platforms: ${{ matrix.architecture.platform }}
           provenance: mode=max
           push: ${{ github.ref_type == 'branch' && github.ref_name == github.event.repository.default_branch }}