fix(theme): fix DocsVersionDropdownNavbarItem version link target

[slorber]

Motivation

Fix #10206

This ensures that the version dropdown "button" and the list item element are consistent and link to the same URL (the current doc, in that version)

Previously, the "button" would link to the root of the docs while the list item would link to the doc.

Test Plan

preview

Test links

https://deploy-preview-10288--docusaurus-2.netlify.app/

[netlify]

✅ [V2]

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[github-actions]

⚡️ Lighthouse report for the deploy preview of this PR

URL	Performance	Accessibility	Best Practices	SEO	Report
/	🔴 39	🟢 98	🟢 100	🟢 100	Report
/docs/installation	🟠 69	🟢 97	🟢 100	🟢 100	Report
/docs/category/getting-started	🟠 75	🟢 100	🟢 100	🟠 86	Report
/blog	🟠 68	🟢 100	🟢 100	🟠 86	Report
/blog/preparing-your-site-for-docusaurus-v3	🔴 48	🟢 96	🟢 100	🟢 100	Report
/blog/tags/release	🟠 70	🟢 100	🟢 100	🟠 86	Report
/blog/tags	🟠 74	🟢 100	🟢 100	🟠 86	Report