Bump lxml from 4.6.3 to 4.6.4 (#231)

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]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

requirements.txt

@@ -12,7 +12,7 @@ future-annotations==1.0.0
 html5lib==1.1
 idna==3.3
 Jinja2==3.0.2
-lxml==4.6.3
+lxml==4.6.4
 MarkupSafe==2.0.1
 mock==4.0.3
 multidict==5.2.0