fix: use the source project to generate commit links for un-persisted merge requests

What does this MR do?

Commit links should point to source_project instead of target_project or it will get 404 when clicking on the MR commits.

This modification check if the commit is showing a non persisted merge request. If it is, the commit link should be point to the source project.

Screenshots

It should point to chiehmin18/gitlab instead of gitlab-org/gitlab

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