Resolve "Unable to edit squash commit message when squashing is required in MRs"

What does this MR do?

Fixes a regression where the edit squashed message input does not appear. See screenshots below.

Screenshots (strongly suggested)

Before	After

Does this MR meet the acceptance criteria?

Conformity

• I have included a changelog entry, or it's not needed. (Does this MR need a changelog?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)

Related to #323498 (closed)