Build(deps-dev): bump tox from 4.21.1 to 4.21.2 (#171)

Bumps [tox](https://github.com/tox-dev/tox) from 4.21.1 to 4.21.2.
<details>
<summary>Release notes</summary>
<p><em>Sourced from <a
href="https://github.com/tox-dev/tox/releases">tox's
releases</a>.</em></p>
<blockquote>
<h2>4.21.2</h2>
<!-- raw HTML omitted -->
<h2>What's Changed</h2>
<ul>
<li>Update sdist rules to include <code>tox.toml</code> (<a
href="https://redirect.github.com/tox-dev/tox/issues/3389">#3389</a>) by
<a href="https://github.com/mgorny"><code>@​mgorny</code></a> in <a
href="https://redirect.github.com/tox-dev/tox/pull/3390">tox-dev/tox#3390</a></li>
</ul>
<p><strong>Full Changelog</strong>: <a
href="https://github.com/tox-dev/tox/compare/4.21.1...4.21.2">https://github.com/tox-dev/tox/compare/4.21.1...4.21.2</a></p>
</blockquote>
</details>
<details>
<summary>Changelog</summary>
<p><em>Sourced from <a
href="https://github.com/tox-dev/tox/blob/main/docs/changelog.rst">tox's
changelog</a>.</em></p>
<blockquote>
<h2>v4.21.2 (2024-10-03)</h2>
<p>Bugfixes - 4.21.2</p>
<pre><code>- Include ``tox.toml`` in sdist archives to fix test failures
resulting from its lack.
  - by :user:`mgorny` (:issue:`3389`)
</code></pre>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.com/tox-dev/tox/commit/c953f4f4ba1e0e7a69de1ecea94e4bdb5a797ac1"><code>c953f4f</code></a>
release 4.21.2</li>
<li><a
href="https://github.com/tox-dev/tox/commit/3ab1d3e559ebea0dac8ae34262158c7234e44997"><code>3ab1d3e</code></a>
Update sdist rules to include <code>tox.toml</code> (<a
href="https://redirect.github.com/tox-dev/tox/issues/3389">#3389</a>)
(<a
href="https://redirect.github.com/tox-dev/tox/issues/3390">#3390</a>)</li>
<li><a
href="https://github.com/tox-dev/tox/commit/172a952f2acf66cfab69558325217a52b387446a"><code>172a952</code></a>
Fix user guide typo</li>
<li>See full diff in <a
href="https://github.com/tox-dev/tox/compare/4.21.1...4.21.2">compare
view</a></li>
</ul>
</details>
<br />


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</details>

pyproject.toml

@@ -73,7 +73,7 @@ optional = true
 [tool.poetry.group.tests.dependencies]
 pytest = "^8.3.3"
 pytest-cov = "^5.0.0"
-tox = "^4.21.1"
+tox = "^4.21.2"
 tox-gh-actions = "^3.2.0"