Run current merge request tests only for changes specific to merge requests apis.

Currently CPT runs the following tests

• group_merge_request - /api/${apiVersion}/groups/${groupId}/merge_requests)
• project_merge_request - /api/${apiVersion}/project/${projectId}/merge_requests

These tests runs for any backend changes by using the patterns that match the files changed related to backend.

This causes noise on MRs which doesn't have code changes which are impacting these tests.

As a part of this issue, identify patterns that would match files that are only related to these two tests.