fix(utils): allow partially backticked markdown h1 contentTitles

[JoshuaKGoldberg]

Pre-flight checklist

• I have read the Contributing Guidelines on pull requests.
• If this is a code change: I have written unit tests and/or added dogfooding pages to fully verify the new behavior.
• If this is a new API or substantial change: the PR has an accompanying issue (closes #0000) and the maintainers have approved on my working plan.

Motivation

See #8294 - I want h1s with inline code please 😄

Test Plan

I ... don't have one beyond unit tests.

Test links

Deploy preview: https://deploy-preview-_____--docusaurus-2.netlify.app/

Related issues/PRs

#8294 - would you like me to file an issue? Or can someone convert that to one?

[netlify]

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[github-actions]

⚡️ Lighthouse report for the deploy preview of this PR

URL	Performance	Accessibility	Best Practices	SEO	PWA	Report
/	🟠 78	🟢 97	🟢 100	🟢 100	🟢 90	Report
/docs/installation	🟠 70	🟢 100	🟢 100	🟢 100	🟢 90	Report

[Josh-Cena]

Fun, isn't this function only used for sanitizing metadata like browser tab title? Does it work when rendering?

[JoshuaKGoldberg]

Yeah, this is a start, but I want to try more. Just blocked on #8315 for testing page changes 😄

[JoshuaKGoldberg]

Or, I guess while that gets worked on, can we get this as a partial fix in the meantime? I think this will at least partially improve the situation?

[slorber]

👍 thanks

Looks like it's working as we want it to: