Fix missing triple``` characters in markdown-features.mdx

[heysokam]

Sorry to be blunt, but I'm not gonna spend +1-2h reading the PR rules just to send such a simple fix.
I'm just fixing missing ``` characters.
Take it or leave it. I don't care either way.

Feel free to fix this in the proper way in a different PR or something, and remove/close this one, if the rules are strict enough for this to not be allowed at all.

Erroring output, without ```

Expected output, with ```

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[github-actions]

⚡️ Lighthouse report for the deploy preview of this PR

URL	Performance	Accessibility	Best Practices	SEO	PWA	Report
/	🟠 60	🟢 98	🟢 100	🟢 100	🟠 89	Report
/docs/installation	🟠 82	🟢 98	🟢 100	🟢 100	🟠 89	Report
/docs/category/getting-started	🟠 75	🟢 100	🟢 100	🟢 90	🟠 89	Report
/blog	🟢 93	🟢 100	🟢 100	🟢 90	🟠 89	Report
/blog/preparing-your-site-for-docusaurus-v3	🟠 64	🟢 97	🟢 100	🟢 100	🟠 89	Report
/blog/tags/release	🟠 70	🟢 100	🟢 100	🟠 80	🟠 89	Report
/blog/tags	🟠 73	🟢 100	🟢 100	🟢 90	🟠 89	Report

[slorber]

thanks for reporting the problem

However it's technically impossible for me to merge if you don't sign the CLA, so let me know if you want to proceed. Otherwise I'll open another pr myself.

[slorber]

Going to open another pr based on yours because cla is not signed and I have other tiny edits to the template to make

BTW using indentation doesn't work anymore for code blocks, cf the result of your PR still not looking great:

[slorber]

will be fixed in #9696 and you'll be credited