Bump lxml from 4.6.3 to 4.9.1

Bumps [lxml](https://github.com/lxml/lxml) from 4.6.3 to 4.9.1.
- [Release notes](https://github.com/lxml/lxml/releases)
- [Changelog](https://github.com/lxml/lxml/blob/master/CHANGES.txt)
- [Commits](https://github.com/lxml/lxml/compare/lxml-4.6.3...lxml-4.9.1)

---
updated-dependencies:
- dependency-name: lxml
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

requirements.txt

@@ -37,7 +37,7 @@ idna-ssl==1.1.0
 importlib-metadata==1.7.0
 importlib-resources==3.0.0
 Jinja2==2.11.3
-lxml==4.6.3
+lxml==4.9.1
 MarkupSafe==1.1.1
 multidict==4.7.6
 mysqlclient==2.0.1