Remove unnecessary top margin in modal header titles

What does this MR do?

Removes the unnecessary margings from margin headers. This deals with both .modal-title (first example) and .page-title (seconds example)

Before	After

What are the relevant issue numbers?

Closes #55883 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer