Draft: Resolve "Merge request child pipeline is not created when using `only:ref`"

What does this MR do?

Findings

The Ci::Bridge record is successfully created and the downstream pipeline yaml file no longer includes the ref: :only reference because of:

https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/models/ci/bridge.rb#L140

It looks like the created pipeline may not be exposed properly via Ci::PipelinesForMergeRequestFinder?

It also looks like the ref policy is not accounting for parent pipeline sources as Fabio noted.

Issue: #208294 (closed)

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team