Disable pipelines on default branch for non canonical projects

What does this MR do and why?

Disable pipelines on default branch for non canonical projects

We regularly see community contributors running out of pipeline minutes because they forgot to use -o ci.skip while pushing the updated master branch to their fork.

Currently we advise them to switch to the community fork to prevent them to use up their quota again, but that doesn't help them in the current month when they also use CI for other projects in their namespace.

We can disable these pipelines entirely as they serve no purpose on forks. This should help community contributors to not accidentially use up their entire pipeline minutes quota for the rest of the month.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

.gitlab-ci.yml

@@ -98,6 +98,9 @@ workflow:
       variables:
         <<: *next-ruby-variables
         PIPELINE_NAME: 'Scheduled Ruby $RUBY_VERSION $CI_COMMIT_BRANCH branch pipeline'
+    # For `$CI_DEFAULT_BRANCH` branch in forks, don't create a pipeline
+    - if: '$CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH && $CI_PROJECT_NAMESPACE !~ /^gitlab(-org|-cn)?($|\/)/'
+      when: never
     # This work around https://gitlab.com/gitlab-org/gitlab/-/issues/332411 whichs prevents usage of dependency proxy
     # when pipeline is triggered by a project access token.
     - if: '$CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH && $GITLAB_USER_LOGIN =~ /project_\d+_bot\d*/'