Build(deps-dev): bump tox from 4.21.0 to 4.21.1 (#170)

Bumps [tox](https://github.com/tox-dev/tox) from 4.21.0 to 4.21.1.
<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>4.21.1</h2>
<!-- raw HTML omitted -->
<h2>What's Changed</h2>
<ul>
<li>Fix TOML configuration errors by <a
href="https://github.com/gaborbernat"><code>@​gaborbernat</code></a> in
<a
href="https://redirect.github.com/tox-dev/tox/pull/3388">tox-dev/tox#3388</a></li>
</ul>
<p><strong>Full Changelog</strong>: <a
href="https://github.com/tox-dev/tox/compare/4.21.0...4.21.1">https://github.com/tox-dev/tox/compare/4.21.0...4.21.1</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>v4.21.1 (2024-10-02)</h2>
<p>Bugfixes - 4.21.1</p>
<pre><code>- Fix error when using ``requires`` within a TOML
configuration file - by :user:`gaborbernat`. (:issue:`3386`)
- Fix error when using ``deps`` within a TOML configuration file - by
:user:`gaborbernat`. (:issue:`3387`)
- Multiple fixes for the TOML configuration by :user:`gaborbernat`.:
<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,<br />
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>)<br />
</code></pre></li>
</ul>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<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>See full diff in <a
href="https://github.com/tox-dev/tox/compare/4.21.0...4.21.1">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 = "^4.21.0"
+tox = "^4.21.1"
 tox-gh-actions = "^3.2.0"