ci: Run 'jest:minimal' upon backend changes in MRs

What does this MR do and why?

This changes the jest-minimal and jest rules to run jest-minimal upon backend changes (when MR isn't approved) to improve Time to First Failure.

Validation

1. In !76224 (closed), we touched app/controllers/projects/autocomplete_sources_controller.rb
2. This led to add the fixture files to the "changed files":

   Changed files: app/controllers/projects/autocomplete_sources_controller.rb tmp/tests/frontend/fixtures-ee/autocomplete_sources/labels.json

3. This led to jest-minimal running the related Jest tests: https://gitlab.com/gitlab-org/gitlab/-/jobs/1859078548

   PASS spec/frontend/gfm_auto_complete_spec.js

   and

   Ran all test suites related to files matching /app\/controllers\/projects\/autocomplete_sources_controller.rb|tmp\/tests\/frontend\/fixtures-ee\/autocomplete_sources\/labels.json/i.

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.