Fix wrong changes counter on merge request commit diffs

What does this MR do and why?

Fixes: #483020 (closed)

This MR allows a proper display of changed files when viewing a single commit in an MR.

Screenshots or screen recordings

Before	After
Screen_Recording_2024-11-21_at_12.54.56	Screen_Recording_2024-11-21_at_12.53.09

How to set up and validate locally

1. Open any merge request with at least 2 commits that change a different number of files in each commit (for example 1 file in the first commit, 2 files in the second one)
2. Switch to a commit (using Commits tab) that has a different number of changed files then what an MR has
3. Observe a correct counter on the Changes tab