Follow up to this: #35114

* Previously we were still showing the commit message even after
cancelling amend which was the old commit message.
* This PR fixes that by restoring the commit message to the old state
before the amend begin so that in case user typed a commit message it's
shown if not then it's not.

Before:


https://github.com/user-attachments/assets/e0edcfff-863d-4367-a7c4-8a2998e702ca

After:



https://github.com/user-attachments/assets/9daf9be0-8a3d-4914-91a4-567693711b6b




Release Notes:

- Resolved an issue where cancelling an amend commit would incorrectly
leave the old commit message in the input field. The commit message box
now properly reverts to its pre-amend state.