Enable `assumeImmutableResults` in `app/assets/javascripts/pages/projects/merge_requests/init_merge_request_show.js`

• Set assumeImmutableResults to true in the Apollo provider that's instantiated in app/assets/javascripts/pages/projects/merge_requests/init_merge_request_show.js
• Verify that the app is working properly.
• If needed, update the implementation so that the app works with immutable objects (e.g. leverage immer for cache mutations).