Fix incorrect line height in file header

What does this MR do?

Fix for #281953 (closed).

This fixes the incorrect line-height in file headers when viewing a diff on the MR Overview tab.

Screenshots

before	after

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Code review guidelines
• Style guides

Availability and Testing

• Tested in all supported browsers

Related to #281953 (closed)