Use of ref for the creation of branch

What does this MR do?

Related to gitlab-org/customers-gitlab-com#5964 (closed)

This is a follow-up of !362 (merged)

This job failing as part of our CustomersDot pipeline revealed that the ref keyword argument I introduced in the previous MR needs to be used instead of the static master value in script/pipeline_ref_updater.rb. This error was triggered as a new branch was trying to be created successfully.

Manual test

Run the following:

REF_UPDATE_GITLAB_API_TOKEN=<your_gitlab_token> ruby script/pipeline_ref_updater.rb "gitlab-org/customers-gitlab-com" .gitlab-ci.yml main

to see the pipeline_ref_updater.rb succeeding and creating a new merge request.

After testing this successfully, this following MR was created: https://gitlab.com/gitlab-org/customers-gitlab-com/-/merge_requests/8758 - since it already pinged a few folks from Quality, I'll leave it open and have it reviewed.

Check-list

• Ensure commits include Changelog: trailer
• Verify the change in all affected pipelines.