rustdoc_to_markdown: Clean up heading spacing (#12456)

This PR cleans up the spacing around the Markdown headings in the output
so that they are consistent.

Release Notes:

- N/A

Marshall Bowers committed 2y ago

abec028e58016b07dc2bf6f3b8243963fcb2bd38

Parent: 0888182

Committed by GitHub <noreply@github.com> on 5/29/2024, 10:39:51 PM