Add List merge request diffs API test
Updating existing MR changes API test to use the new endpoint due to deprecation of changes
endpoint in 15.7:
- Updated
api_v4_projects_merge_requests_merge_request_changes
toapi_v4_projects_merge_requests_merge_request_diffs
- Added dynamic endpoint switch between
diffs
andchanges
based on target GitLab version
Closes #547 (closed)