Run tagging job only on default branches

This patch should reduce the need of customizations in downstream
gitlab-ci includes by making the most common case, of running the
container build tagging, only on the default branch of the repository.

gitlab-ci-template.yml

@@ -43,3 +43,5 @@ container-tagging:
     - podman pull "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG-$CI_COMMIT_SHORT_SHA"
     - si-tagging -l "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG-$CI_COMMIT_SHORT_SHA" "$CI_REGISTRY_IMAGE" "${CI_REGISTRY_IMAGE_VERSION}"
     - si-push "$CI_REGISTRY_IMAGE"
+  workflow:
+    if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH