🛠 Repo: CHANGELOG.md accessibility issues: headings

[JoshuaKGoldberg]

Tooling Suggestion Checklist

• I have tried restarting my IDE and the issue persists.
• I have pulled the latest master branch of the repository.
• I have read and agree to Mocha's Code of Conduct and Contributing Guidelines
• I have searched for related issues and issues with the faq label, but none matched my issue.
• I want to provide a PR to resolve this

Overview

Right now the CHANGELOG.md file is manually edited to have many # h1s. Although crawlers such as Google's can handle them, it's generally accessibility best practice not to in straightforward pages such as a changelog (e.g. https://www.a11yproject.com/posts/how-to-accessible-heading-structure/#one-h1). Instead we should have a single # Changelog h1 followed by h2s for each entry.

Additional Info

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