Build: Bump cython from 3.1.4 to 3.1.5 (#2647)

Bumps [cython](https://github.com/cython/cython) from 3.1.4 to 3.1.5.
<details>
<summary>Release notes</summary>
<p><em>Sourced from <a
href="https://github.com/cython/cython/releases">cython's
releases</a>.</em></p>
<blockquote>
<h1>3.1.5 (2025-10-19)</h1>
<h2>Bugs fixed</h2>
<ul>
<li>
<p>Conversion from C++ strings longer than <code>PY_SSIZE_T_MAX</code>
did not validate the length.</p>
</li>
<li>
<p>Some non-Limited API code was incorrectly used in generated header
files.
(Github issue :issue:<code>7157</code>)</p>
</li>
<li>
<p>Optimised unpacking of Python integers in expressions uses a slightly
safer scheme.
(Github issue :issue:<code>7134</code>)</p>
</li>
<li>
<p>Empty return statements were not always reported when tracing.
(Github issue :issue:<code>7022</code>)</p>
</li>
<li>
<p>Value conversion errors when tracing C return statements no longer
fail the trace
but fall back to reporting <code>None</code> returns instead.
(Github issue :issue:<code>6503</code>)</p>
</li>
</ul>
</blockquote>
</details>
<details>
<summary>Changelog</summary>
<p><em>Sourced from <a
href="https://github.com/cython/cython/blob/master/CHANGES.rst">cython's
changelog</a>.</em></p>
<blockquote>
<h1>3.1.5 (2025-10-20)</h1>
<h2>Bugs fixed</h2>
<ul>
<li>
<p>Conversion from C++ strings longer than <code>PY_SSIZE_T_MAX</code>
did not validate the length.</p>
</li>
<li>
<p>Some non-Limited API code was incorrectly used in generated header
files.
(Github issue :issue:<code>7157</code>)</p>
</li>
<li>
<p>Optimised unpacking of Python integers in expressions uses a slightly
safer scheme.
(Github issue :issue:<code>7134</code>)</p>
</li>
<li>
<p>Empty return statements were not always reported when tracing.
(Github issue :issue:<code>7022</code>)</p>
</li>
<li>
<p>Value conversion errors when tracing C return statements no longer
fail the trace
but fall back to reporting <code>None</code> returns instead.
(Github issue :issue:<code>6503</code>)</p>
</li>
</ul>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.com/cython/cython/commit/24eb0d558efe0a92ba87bb7ebed45c14ed4a713e"><code>24eb0d5</code></a>
Build: Move release step to separate job to enforce complete releases
and cut...</li>
<li><a
href="https://github.com/cython/cython/commit/2dc58ee83b604fd1d66093026501fc23620c839f"><code>2dc58ee</code></a>
Update changelog.</li>
<li><a
href="https://github.com/cython/cython/commit/5f1fa053f1e77b9eb7c5eaf84a46926fd1f5d072"><code>5f1fa05</code></a>
Fix CI for Python 3.14.0 (<a
href="https://redirect.github.com/cython/cython/issues/7197">GH-7197</a>)</li>
<li><a
href="https://github.com/cython/cython/commit/acc3d7c7d88d9fa49e19661121e3ea6fcd4bb356"><code>acc3d7c</code></a>
Adapt some tests to different error messages in Py3.15.</li>
<li><a
href="https://github.com/cython/cython/commit/9143822ee7a24dd336b805e98771c0bcfc1e8590"><code>9143822</code></a>
Replace outdated &quot;codecs.open()&quot; usage with just
&quot;open()&quot;.</li>
<li><a
href="https://github.com/cython/cython/commit/bbe48384586be9c4becda826d8ae8de781fa5d53"><code>bbe4838</code></a>
Prepare release of 3.1.5.</li>
<li><a
href="https://github.com/cython/cython/commit/3bc285ddf68023ac25c542c421ff09171cf88146"><code>3bc285d</code></a>
Upgrade cibuildwheel to latest 3.2.1.</li>
<li><a
href="https://github.com/cython/cython/commit/729dd6c80ed3a0512081c66438699d8245ea87c8"><code>729dd6c</code></a>
Update changelog.</li>
<li><a
href="https://github.com/cython/cython/commit/c4da583e3aef95ebcd4cd0f761d8520413c67c14"><code>c4da583</code></a>
Allow TraceReturnCValue conversion to fail in non-monitoring (<a
href="https://redirect.github.com/cython/cython/issues/7064">#7064</a>)</li>
<li><a
href="https://github.com/cython/cython/commit/dd664381c39579b49c81592e3887cce216b40266"><code>dd66438</code></a>
Fix tracing of empty return statements (<a
href="https://redirect.github.com/cython/cython/issues/7067">GH-7067</a>)</li>
<li>Additional commits viewable in <a
href="https://github.com/cython/cython/compare/3.1.4...3.1.5">compare
view</a></li>
</ul>
</details>
<br />


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