Bump lxml from 4.6.3 to 4.6.4

Bumps [lxml](https://github.com/lxml/lxml) from 4.6.3 to 4.6.4.
- [Release notes](https://github.com/lxml/lxml/releases)
- [Changelog](https://github.com/lxml/lxml/blob/master/CHANGES.txt)
- [Commits](lxml/lxml@lxml-4.6.3...lxml-4.6.4)

---
updated-dependencies:
- dependency-name: lxml
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

test-requirements.txt

@@ -32,7 +32,7 @@ iniconfig==1.1.1
     # via pytest
 jinja2==3.0.2
     # via sphinx
-lxml==4.6.3
+lxml==4.6.4
     # via -r test-requirements.in
 markupsafe==2.0.1
     # via jinja2