Bump lxml from 4.6.2 to 4.6.3 in /desktop/core (#1952)

Bumps [lxml](https://github.com/lxml/lxml) from 4.6.2 to 4.6.3.
<details>
<summary>Changelog</summary>
<p><em>Sourced from <a href="https://github.com/lxml/lxml/blob/master/CHANGES.txt">lxml's changelog</a>.</em></p>
<blockquote>
<h1>4.6.3 (2021-03-21)</h1>
<h2>Bugs fixed</h2>
<ul>
<li>A vulnerability (CVE-2021-28957) was discovered in the HTML Cleaner by Kevin Chung,
which allowed JavaScript to pass through.  The cleaner now removes the HTML5
<code>formaction</code> attribute.</li>
</ul>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a href="https://github.com/lxml/lxml/commit/a5f9cb52079dc57477c460dbe6ba0f775e14a999"><code>a5f9cb5</code></a> Prepare release of lxml 4.6.3.</li>
<li><a href="https://github.com/lxml/lxml/commit/2d01a1ba8984e0483ce6619b972832377f208a0d"><code>2d01a1b</code></a> Add HTML-5 &quot;formaction&quot; attribute to &quot;defs.link_attrs&quot; (<a href="https://github-redirect.dependabot.com/lxml/lxml/issues/316">GH-316</a>)</li>
<li><a href="https://github.com/lxml/lxml/commit/e986a9cb5d54827c59aefa8803bc90954d67221e"><code>e986a9c</code></a> Fix reference in docs.</li>
<li>See full diff in <a href="https://github.com/lxml/lxml/compare/lxml-4.6.2...lxml-4.6.3">compare view</a></li>
</ul>
</details>
<br />


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desktop/core/requirements.txt

@@ -33,7 +33,7 @@ jdcal==1.0.1
 kazoo==2.8.0
 kerberos==1.3.0
 lockfile==0.12.2
-lxml==4.6.2
+lxml==4.6.3
 Mako==1.1.4
 Markdown==3.1
 mysqlclient==1.4.6