Eliminate extra spacing on MR diffs from mobile/tablet screen

What does this MR do?

Eliminates extra spacing on sides of the tab of MR diffs from mobile/tablet screen.

Screenshots

conditions	before	after
Inline (iPhone 8 Plus)
Collapsed (iPhone 8 Plus)	n/a
Inline, collapsed with file tree (iPad Pro)	n/a
Side-by-side diff, collapsed with file tree (iPad Pro)	n/a

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [n/a] Documentation (if required)
• Code review guidelines
• [n/a] Merge request performance guidelines
• Style guides
• [n/a] Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Closes #254197 (closed)