PipelinesFinder use git cached data

What does this MR do?

Avoid git calls and use cache data that probably always is on the cache

What are the relevant issue numbers?

Closes #19318 (closed)

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• [ ] Documentation created/updated
• [ ] API support added
• Tests
  • [ ] Added for this feature/bug
  • All builds are passing
• Conform by the style guides
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together Closes #19318 (closed)

Marked the task CHANGELOG entry added as completed

Marked the task Conform by the style guides as completed

Marked the task Branch has no merge conflicts with master (if you do - rebase it please) as completed

Marked the task Squashed related commits together as completed

Marked the task All builds are passing as completed

Reassigned to @yorickpeterse

@yorickpeterse I was navigating the code and just found this usage, not in the sprint but would be great to have if merged

Milestone changed to %8.10

Added ~18308 label

Status changed to merged

mentioned in commit 10232896

mentioned in merge request gitlab-com/www-gitlab-com!2497 (merged)