Add merge request header branch actions left margin
What does this MR do?
Adds left margin to the merge request header branch actions.
Screenshots (if relevant)
Does this MR meet the acceptance criteria?
- Changelog entry added, if necessary
- Conform to the code review guidelines
- Has been reviewed by a UX Designer
- Has been reviewed by a Frontend maintainer
What are the relevant issue numbers?
Closes #49238 (closed)