Show existing MRs in blob commit change modal
<!--IssueSummary start--> <details> <summary> Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards. </summary> - [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=499292) </details> <!--IssueSummary end--> context: https://gitlab.com/gitlab-org/gitlab/-/issues/444302#note_2159015811 ## Proposed solution Check if a file has been modified in existing MRs and show it in the modal
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