Bump site-shared from b2ffb98 to 6231834 (#11909)

Bumps [site-shared](https://github.com/dart-lang/site-shared) from
`b2ffb98` to `6231834`.
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.com/dart-lang/site-shared/commit/6231834a7a44cf6d3f48ec2b5c316671de6e69ac"><code>6231834</code></a>
Bump actions/cache from 4.2.2 to 4.2.3 in the github-actions group (<a
href="https://redirect.github.com/dart-lang/site-shared/issues/241">#241</a>)</li>
<li>See full diff in <a
href="https://github.com/dart-lang/site-shared/compare/b2ffb98eaf2d4022ebfc8ceb0af268f2e6449d13...6231834a7a44cf6d3f48ec2b5c316671de6e69ac">compare
view</a></li>
</ul>
</details>
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