Re-instate: Unnecessary suggestion to fork when editing file on commit tree

This MR had to be reverted due to MVC mismatch. In order to comply with MVC, the front and backend bits of code adding a new GraphQL field have to be in separate MRs in separate milestones.

See !159557 (comment 2023596851) for context around the error.

cc @psjakubowska for 👀