Prevent "nonewline" type diff lines from showing a diff unfolding link

What does this MR do?

Fixes a bug in which "nonewline" diff lines contained an ellipsis-link to unfold diff lines. This bug is only present in the parallel (side-by-side) view.

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

To test, one easy place to find this bug is to look at the following diff view in the GDK:

http://localhost:3000/gitlab-org/gitlab-test/compare/feature_conflict...master?view=parallel

Check out "with space/README.md" at the bottom.

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 #26829 (closed)