Resolve "Commit messages are no longer monospace, but still white-space: pre-wrap"

What does this MR do?

This updates the way commit descriptions are displayed across GitLab:

• Monospace font.
• Overflow-x with scroll bar.

There is an EE port for this:

• gitlab-ee!6770

Why was this MR needed?

• #47548 (closed)

Screenshots (if relevant)

Here's a gif of the commit page:

Here's some screenshots of what this looks like across the application:

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [ ] Documentation created/updated
• [ ] API support added
• [ ] Tests added for this feature/bug
• Conforms to the code review guidelines
  • Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
  • [ ] Has been reviewed by a Backend maintainer
  • [ ] Has been reviewed by a Database specialist
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Closes #47548 (closed)