Resolve "ActionView::Template::Error: 4:Deadline Exceeded."

What

method ipynb? was loading the diff before it was needed, causing performance issues.

How to reproduce

1. Navigate to http://gdk.test:3000/gitlab-org/gitlab-shell/-/compare/13-18-stable...main?from_project_id=2
2. You should see an error on master, no error on this branch

Related to #357535 (closed)