Resolve "Cancel automatic merge button gets a bigger height than it should when content overflows"

What does this MR do?

Fix stretched buttons
Remove unnecessary flexbox utility css class

Are there points in the code the reviewer needs to double check?

Do not believe so

Screenshots (if relevant)

Before:

After:

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Conform by the code review guidelines
  • Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
• Conform by the style guides

What are the relevant issue numbers?

Closes #42677 (closed)