Clicking "Discard" on a file's change in WebIDE does nothing.

Summary

If you click "Discard" on a file's change, whether it is staged or not, nothing happens.

Steps to reproduce

1. Open any file in the Web IDE.
2. Make a small change.
3. Click "Commit" at the bottom left.
4. When the diff view shows up. Click "Discard".

The changes in that file are not discarded.

"Discard All Changes" however works just fine.

I found this issue while testing !19339 (merged) on Staging and I thought it was a regression, but it is also currently present on GitLab.com.

What is the current bug behavior?

The changes are not discarded.

What is the expected correct behavior?

The changes should be discarded

Relevant logs and/or screenshots

Discard_doesnt_work

Output of checks

This bug happens on GitLab.com.a