Don't run the Diff function on all commits in the beforeHook

Tucker McKnight <tmcknight@instructure.com> | Sat Oct 03 2026

Don't run the Diff function on all commits in the beforeHook

To save on the amount of time and memory that the beforeHook takes,
only run Diff when getting the actual diff for the commit.ts page.
We don't need the html-marked-up strings in the beforeHook, we
only need that when rendering the pages.

This unfortunately does not stop it from running out of memory
on larger repos. I suspect that it does save *some* memory, though.