Bump rdoc from 6.8.0 to 6.8.1 (#4078)

Bumps [rdoc](https://github.com/ruby/rdoc) from 6.8.0 to 6.8.1.
<details>
<summary>Release notes</summary>
<p><em>Sourced from <a
href="https://github.com/ruby/rdoc/releases">rdoc's
releases</a>.</em></p>
<blockquote>
<h2>v6.8.1</h2>
<!-- raw HTML omitted -->
<h2>What's Changed</h2>
<h3>🐛 Bug Fixes</h3>
<ul>
<li>Added missing _sidebar_toggle.rhtml by <a
href="https://github.com/ishe-ua"><code>@​ishe-ua</code></a> in <a
href="https://redirect.github.com/ruby/rdoc/pull/1211">ruby/rdoc#1211</a></li>
</ul>
<h2>New Contributors</h2>
<ul>
<li><a href="https://github.com/ishe-ua"><code>@​ishe-ua</code></a> made
their first contribution in <a
href="https://redirect.github.com/ruby/rdoc/pull/1211">ruby/rdoc#1211</a></li>
</ul>
<p><strong>Full Changelog</strong>: <a
href="https://github.com/ruby/rdoc/compare/v6.8.0...v6.8.1">https://github.com/ruby/rdoc/compare/v6.8.0...v6.8.1</a></p>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.com/ruby/rdoc/commit/9a7ab17f401cb92aa33ac903dc614d437e91e5e3"><code>9a7ab17</code></a>
Bump version to v6.8.1</li>
<li><a
href="https://github.com/ruby/rdoc/commit/10596827f04268fb065c8b9a550754b19d47ebc5"><code>1059682</code></a>
Update rdoc.gemspec (<a
href="https://redirect.github.com/ruby/rdoc/issues/1211">#1211</a>)</li>
<li>See full diff in <a
href="https://github.com/ruby/rdoc/compare/v6.8.0...v6.8.1">compare
view</a></li>
</ul>
</details>
<br />


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Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Gemfile.lock

@@ -360,7 +360,7 @@ GEM
       ffi (~> 1.0)
     rbs (3.6.1)
       logger
-    rdoc (6.8.0)
+    rdoc (6.8.1)
       psych (>= 4.0.0)
     redis (5.3.0)
       redis-client (>= 0.22.0)