Fix text overflow

What does this MR do?

In side by side diffs, the text will break line in order to be readable.

This is just a fix for side by side MR comments on desktop, it does not fix this view in mobile. See this issue for more information: https://gitlab.com/gitlab-org/gitlab-ce/issues/26003

Screenshots (if relevant)

Before:

After:

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #25930 (closed)