docs: fix 3.2 blog post headings

[slorber]

Headings in #10000 are not good

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[github-actions]

⚡️ Lighthouse report for the deploy preview of this PR

URL	Performance	Accessibility	Best Practices	SEO	PWA	Report
/	🔴 49	🟢 98	🟢 96	🟢 100	🟠 88	Report
/docs/installation	🟠 51	🟢 96	🟢 100	🟢 100	🟠 88	Report
/docs/category/getting-started	🟠 75	🟢 100	🟢 100	🟢 90	🟠 88	Report
/blog	🟠 69	🟢 100	🟢 100	🟢 90	🟠 88	Report
/blog/preparing-your-site-for-docusaurus-v3	🟠 62	🟢 96	🟢 100	🟢 100	🟠 88	Report
/blog/tags/release	🟠 70	🟢 100	🟢 100	🟠 80	🟠 88	Report
/blog/tags	🟠 76	🟢 100	🟢 100	🟢 90	🟠 88	Report

[github-actions]

Size Change: 0 B

Total Size: 1.05 MB

ℹ️ View Unchanged

Filename	Size
website/.docusaurus/globalData.json	91.2 kB
website/build/assets/css/styles.********.css	114 kB
website/build/assets/js/main.********.js	809 kB
website/build/index.html	38 kB

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