fix: make linguist ignore mdx

[nexxeln]

✅ Checklist

• I have followed every step in the contributing guide (updated 2022-10-06).
• The PR title follows the convention we established conventional-commit
• I performed a functional test on my final commit

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Changelog

This is not an MDX repo

[changeset-bot]

⚠️ No Changeset found

Latest commit: e33a041

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[vercel]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Updated (UTC)
create-t3-app	✅ Ready (Inspect)	Visit Preview	Jun 30, 2023 8:48am
t3-upgrade	✅ Ready (Inspect)	Visit Preview	Jun 30, 2023 8:48am

[github-actions]

⚡️ Lighthouse report for the changes in this PR:

Category	Score
🟢 Performance	98
🟢 Accessibility	100
🟢 Best practices	100
🟢 SEO	100
🔴 PWA	30

Lighthouse ran on https://create-t3-app-git-ignore-mdx-t3-oss.vercel.app/

[c-ehrlich]

Good call