Bump multidict from 5.0.2 to 5.1.0 (#549)

Bumps [multidict](https://github.com/aio-libs/multidict) from 5.0.2 to 5.1.0.
<details>
<summary>Release notes</summary>
<p><em>Sourced from <a href="https://github.com/aio-libs/multidict/releases">multidict's releases</a>.</em></p>
<blockquote>
<h2>multidict 5.1.0 release</h2>
<h1>Changes</h1>
<h2>Features</h2>
<ul>
<li>Support <code>GenericAliases</code> (<code>MultiDict[str]</code>) for Python 3.9+
<code>[#553](aio-libs/multidict#553) &lt;https://github.com/aio-libs/multidict/issues/553&gt;</code>_</li>
</ul>
<h2>Bugfixes</h2>
<ul>
<li>Synchronize the declared supported Python versions in <code>setup.py</code> with actually supported and tested ones.
<code>[#552](aio-libs/multidict#552) &lt;https://github.com/aio-libs/multidict/issues/552&gt;</code>_</li>
</ul>
</blockquote>
</details>
<details>
<summary>Changelog</summary>
<p><em>Sourced from <a href="https://github.com/aio-libs/multidict/blob/master/CHANGES.rst">multidict's changelog</a>.</em></p>
<blockquote>
<h1>5.1.0 (2020-12-03)</h1>
<h2>Features</h2>
<ul>
<li>Support <code>GenericAliases</code> (<code>MultiDict[str]</code>) for Python 3.9+
<code>[#553](aio-libs/multidict#553) &lt;https://github.com/aio-libs/multidict/issues/553&gt;</code>_</li>
</ul>
<h2>Bugfixes</h2>
<ul>
<li>Synchronize the declared supported Python versions in <code>setup.py</code> with actually supported and tested ones.
<code>[#552](aio-libs/multidict#552) &lt;https://github.com/aio-libs/multidict/issues/552&gt;</code>_</li>
</ul>
<hr />
<h1>5.0.1 (2020-11-14)</h1>
<h2>Bugfixes</h2>
<ul>
<li>Provide x86 Windows wheels
<code>[#550](aio-libs/multidict#550) &lt;https://github.com/aio-libs/multidict/issues/550&gt;</code>_</li>
</ul>
<hr />
<h1>5.0.0 (2020-10-12)</h1>
<h2>Features</h2>
<ul>
<li>Provide wheels for <code>aarch64</code>, <code>i686</code>, <code>ppc64le</code>, <code>s390x</code> architectures on Linux
as well as <code>x86_64</code>.
<code>[#500](aio-libs/multidict#500) &lt;https://github.com/aio-libs/multidict/issues/500&gt;</code>_</li>
<li>Provide wheels for Python 3.9.
<code>[#534](aio-libs/multidict#534) &lt;https://github.com/aio-libs/multidict/issues/534&gt;</code>_</li>
</ul>
<h2>Removal</h2>
<ul>
<li>Drop Python 3.5 support; Python 3.6 is the minimal supported Python version.</li>
</ul>
<!-- raw HTML omitted -->
</blockquote>
<p>... (truncated)</p>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a href="https://github.com/aio-libs/multidict/commit/c3eed831bb8bb944bb329013b4fd4b02c66fbf18"><code>c3eed83</code></a> Bump to 5.1.0</li>
<li><a href="https://github.com/aio-libs/multidict/commit/14f433da3b6fd7c443cf85882a6dd1016427262b"><code>14f433d</code></a> Support GenericAliases for Python 3.9+ (<a href="https://github-redirect.dependabot.com/aio-libs/multidict/issues/553">#553</a>)</li>
<li><a href="https://github.com/aio-libs/multidict/commit/e19929eade3571c154b7a6afd57be0360e4a455a"><code>e19929e</code></a> Fix github workflow filter</li>
<li><a href="https://github.com/aio-libs/multidict/commit/b92ea7f32198107f320c56fcfc17bf3b1ea963e1"><code>b92ea7f</code></a> Drop Python 3.5 from setup.py (<a href="https://github-redirect.dependabot.com/aio-libs/multidict/issues/552">#552</a>)</li>
<li>See full diff in <a href="https://github.com/aio-libs/multidict/compare/v5.0.2...v5.1.0">compare view</a></li>
</ul>
</details>
<br />


[![Dependabot compatibility score](https://dependabot-badges.githubapp.com/badges/compatibility_score?dependency-name=multidict&package-manager=pip&previous-version=5.0.2&new-version=5.1.0)](https://docs.github.com/en/github/managing-security-vulnerabilities/configuring-github-dependabot-security-updates)

Dependabot will resolve any conflicts with this PR as long as you don't alter it yourself. You can also trigger a rebase manually by commenting `@dependabot rebase`.

[//]: # (dependabot-automerge-start)
[//]: # (dependabot-automerge-end)

requirements/test.txt

@@ -1,6 +1,6 @@
 pytest-cov>=2.3.1
 pytest==6.2.0
-multidict==5.0.2
+multidict==5.1.0
 idna==2.10
 typing_extensions==3.7.4.2;python_version<"3.8"
 -e .