Bump pip from 21.3 to 21.3.1 in /.github/workflows (#67)

Bumps [pip](https://github.com/pypa/pip) from 21.3 to 21.3.1.
<details>
<summary>Changelog</summary>
<p><em>Sourced from <a href="https://github.com/pypa/pip/blob/main/NEWS.rst">pip's changelog</a>.</em></p>
<blockquote>
<h1>21.3.1 (2021-10-22)</h1>
<h2>Bug Fixes</h2>
<ul>
<li>Always refuse installing or building projects that have no <code>pyproject.toml</code> nor
<code>setup.py</code>. (<code>[#10531](pypa/pip#10531) &lt;https://github.com/pypa/pip/issues/10531&gt;</code>_)</li>
<li>Tweak running-as-root detection, to check <code>os.getuid</code> if it exists, on Unix-y and non-Linux/non-MacOS machines. (<code>[#10565](pypa/pip#10565) &lt;https://github.com/pypa/pip/issues/10565&gt;</code>_)</li>
<li>When installing projects with a <code>pyproject.toml</code> in editable mode, and the build
backend does not support :pep:<code>660</code>, prepare metadata using
<code>prepare_metadata_for_build_wheel</code> instead of <code>setup.py egg_info</code>. Also, refuse
installing projects that only have a <code>setup.cfg</code> and no <code>setup.py</code> nor
<code>pyproject.toml</code>. These restore the pre-21.3 behaviour. (<code>[#10573](pypa/pip#10573) &lt;https://github.com/pypa/pip/issues/10573&gt;</code>_)</li>
<li>Restore compatibility of where configuration files are loaded from on MacOS (back to <code>Library/Application Support/pip</code>, instead of <code>Preferences/pip</code>). (<code>[#10585](pypa/pip#10585) &lt;https://github.com/pypa/pip/issues/10585&gt;</code>_)</li>
</ul>
<h2>Vendored Libraries</h2>
<ul>
<li>Upgrade pep517 to 0.12.0</li>
</ul>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a href="https://github.com/pypa/pip/commit/f9914f3ebe223004b1d439a2b1980bd132d14f27"><code>f9914f3</code></a> Bump for release</li>
<li><a href="https://github.com/pypa/pip/commit/f9f2db248fc04b46bd0149eba92882e4932c627e"><code>f9f2db2</code></a> Update AUTHORS.txt</li>
<li><a href="https://github.com/pypa/pip/commit/f2d776be2adffee700ef4563893dc01dc231125c"><code>f2d776b</code></a> Merge pull request <a href="https://github-redirect.dependabot.com/pypa/pip/issues/10607">#10607</a> from pradyunsg/fix-docs-builds</li>
<li><a href="https://github.com/pypa/pip/commit/4a4b613a7ccdf4c4aab8f223f9b97f413b8b3056"><code>4a4b613</code></a> Merge PR <a href="https://github-redirect.dependabot.com/pypa/pip/issues/10577">#10577</a> from sbidoul/fix-pep660-metadata-preparation-fallback</li>
<li><a href="https://github.com/pypa/pip/commit/f4d67ba0c091c5b02096ddb211c7602bf0d95580"><code>f4d67ba</code></a> Merge pull request <a href="https://github-redirect.dependabot.com/pypa/pip/issues/10592">#10592</a> from pradyunsg/update-ewdurbin-name</li>
<li><a href="https://github.com/pypa/pip/commit/37aef106a325ed7b1115f04028360e03dbfe7ee8"><code>37aef10</code></a> Merge pull request <a href="https://github-redirect.dependabot.com/pypa/pip/issues/10536">#10536</a> from pradyunsg/docs/fix-wordin</li>
<li><a href="https://github.com/pypa/pip/commit/457564cf38ad5da75672d4de119e4c5ae19fbd56"><code>457564c</code></a> Merge pull request <a href="https://github-redirect.dependabot.com/pypa/pip/issues/10585">#10585</a> from pradyunsg/fix-config-paths</li>
<li><a href="https://github.com/pypa/pip/commit/8c1f333ba5cb0a8c2cc4c775355bdde4ae06e50f"><code>8c1f333</code></a> Merge pull request <a href="https://github-redirect.dependabot.com/pypa/pip/issues/10580">#10580</a> from pradyunsg/better-towncrier-template</li>
<li><a href="https://github.com/pypa/pip/commit/cc559ed6237f7461c919d403c93fbc2ac82abe09"><code>cc559ed</code></a> Merge pull request <a href="https://github-redirect.dependabot.com/pypa/pip/issues/10583">#10583</a> from pradyunsg/fix-vendoring</li>
<li><a href="https://github.com/pypa/pip/commit/0c2574b7ef78791dd98822bca038b6d839b5378c"><code>0c2574b</code></a> Merge pull request <a href="https://github-redirect.dependabot.com/pypa/pip/issues/10566">#10566</a> from n1000/dont_warn_on_bsd</li>
<li>See full diff in <a href="https://github.com/pypa/pip/compare/21.3...21.3.1">compare view</a></li>
</ul>
</details>
<br />


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</details>

.github/workflows/constraints.txt

@@ -1,4 +1,4 @@
-pip==21.3
+pip==21.3.1
 nox==2021.10.1
 nox-poetry==0.8.6
 poetry==1.1.11