chore(deps-dev): Update tox requirement from 4.20.0 to 4.21.2 (#808)

Updates the requirements on [tox](https://github.com/tox-dev/tox) to
permit the latest version.
<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`)
<h2>v4.21.1 (2024-10-02)</h2>
<p>Bugfixes - 4.21.1
</code></pre></p>
<ul>
<li>
<p>Fix error when using <code>requires</code> within a TOML
configuration file - by :user:<code>gaborbernat</code>.
(:issue:<code>3386</code>)</p>
</li>
<li>
<p>Fix error when using <code>deps</code> within a TOML configuration
file - by :user:<code>gaborbernat</code>. (:issue:<code>3387</code>)</p>
</li>
<li>
<p>Multiple fixes for the TOML configuration by
:user:<code>gaborbernat</code>.:</p>
<ul>
<li>Do not fail when there is an empty command within
<code>commands</code>.</li>
<li>Allow references for <code>set_env</code> by accepting list of
dictionaries for it.</li>
<li>Do not try to be smart about reference unrolling, instead allow the
user to control it via the <code>extend</code> flag,
available both for <code>posargs</code> and <code>ref</code>
replacements.</li>
<li>The <code>ref</code> replacements <code>raw</code> key has been
renamed to <code>of</code>. (:issue:<code>3388</code>)</li>
</ul>
</li>
</ul>
<h2>v4.21.0 (2024-09-30)</h2>
<p>Features - 4.21.0</p>
<pre><code>- Native TOML configuration support - by :user:`gaborbernat`.
(:issue:`999`)
<p>Improved Documentation - 4.21.0
</code></pre></p>
<ul>
<li>Update Loader docs - by :user:ziima (:issue:<code>3352</code>)</li>
</ul>
<h2>v4.20.0 (2024-09-18)</h2>
<p>Features - 4.20.0</p>
<pre><code>- Separate the list dependencies functionality to a separate
abstract class allowing code reuse in plugins (such as
  ``tox-uv``) - by :gaborbernat`. (:issue:`3347`)
<h2>v4.19.0 (2024-09-17)</h2>
<p>Features - 4.19.0
</code></pre></p>
<ul>
<li>Support <code>pypy-&lt;major&gt;.&lt;minor&gt;</code> environment
names for PyPy environments - by :user:<code>gaborbernat</code>.
(:issue:<code>3346</code>)</li>
</ul>
<p>v4.18.1 (2024-09-07)</p>
<!-- raw HTML omitted -->
</blockquote>
<p>... (truncated)</p>
</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><a
href="https://github.com/tox-dev/tox/commit/434ac18d89a843b961c8544bf74e796191c940f0"><code>434ac18</code></a>
release 4.21.1</li>
<li><a
href="https://github.com/tox-dev/tox/commit/34d3adc0ed537de5d4803b4e244e43eed513c839"><code>34d3adc</code></a>
Fix TOML configuration errors (<a
href="https://redirect.github.com/tox-dev/tox/issues/3388">#3388</a>)</li>
<li><a
href="https://github.com/tox-dev/tox/commit/719b3462b58bd5c4fc12d93cb978f824bc7a610b"><code>719b346</code></a>
Update installation.rst</li>
<li><a
href="https://github.com/tox-dev/tox/commit/46bef9eff54c53eeced031436d2d1a068b4bfb16"><code>46bef9e</code></a>
release 4.21.0</li>
<li><a
href="https://github.com/tox-dev/tox/commit/cea105b7007039c830c92ae92aa5792e819ee487"><code>cea105b</code></a>
True TOML config support (<a
href="https://redirect.github.com/tox-dev/tox/issues/3353">#3353</a>)</li>
<li><a
href="https://github.com/tox-dev/tox/commit/a04b039fe0486752ec79733b993d73ecdf282795"><code>a04b039</code></a>
[pre-commit.ci] pre-commit autoupdate (<a
href="https://redirect.github.com/tox-dev/tox/issues/3385">#3385</a>)</li>
<li><a
href="https://github.com/tox-dev/tox/commit/f5eba31ed3aeedcb41db64fca5b624a75abff32d"><code>f5eba31</code></a>
Update Loader docs (<a
href="https://redirect.github.com/tox-dev/tox/issues/3352">#3352</a>)</li>
<li>Additional commits viewable in <a
href="https://github.com/tox-dev/tox/compare/4.20.0...4.21.2">compare
view</a></li>
</ul>
</details>
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pyproject.toml

@@ -92,7 +92,7 @@ isort = "5.13.2"
 autopep8 = "2.3.1"
 mypy = "1.11.2"
 bandit = "1.7.10"
-tox = "4.20.0"
+tox = "4.21.2"
 # min version required to be able to install some dependencies
 # see https://github.com/MichaelKim0407/flake8-use-fstring/issues/33
 setuptools = ">= 47.0.0"