Fix alignment of diff system note icons

What does this MR do and why?

Fixes vertical alignment of system notes on diffs

What does this MR not fix?

Inconsistent indentation between changes and overview tabs

Screenshots or screen recordings

	Before	After
Diff activity on Overview tab
Diff activity on Changes tab

How to set up and validate locally

• Go to MR
• Comment on line of code
• Resolve using Create issue to resolve button
• Add another comment to thread
• Check thread on both Overview and Changes tabs

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.