[mutter] ci: Rename only_default to pipeline_guard

[Marge Bot <marge-bot src gnome org>]

commit 6b220c9c37969399ac6fdf139ed5224f3a47dde2
Author: Jonas Ådahl <jadahl gmail com>
Date:   Fri Nov 20 19:07:29 2020 +0100

    ci: Rename only_default to pipeline_guard
    
    It's the rules that guard the pipelines, deciding when they are allowed
    to run or not. The 'only_default' comes from the fact that in the past
    they set the only: field.
    
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1588>

 .gitlab-ci.yml | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 28de19cac9..dac62e2632 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -58,7 +58,7 @@ workflow:
     - if: '$CI_COMMIT_TAG'
     - if: '$CI_COMMIT_BRANCH'
 
-.only_default: &only_default
+.pipline-guard: &pipline-guard
   rules:
     - if: '$CI_PIPELINE_SOURCE == "merge_request_event"'
     - if: '$CI_COMMIT_TAG'
@@ -74,7 +74,7 @@ build-fedora-container:
   needs:
     - check-commit-log
     - check-merge-request
-  <<: *only_default
+  &pipline-guard
 
 check-commit-log:
   extends: