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](lxml/lxml@lxml-4.6.3...lxml-4.9.1)

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

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

Author: dependabot[bot]

requirements.txt

@@ -33,7 +33,7 @@ itsdangerous==0.24
 Jinja2==2.11.3
 json-cfg==0.4.2
 kwonly-args==1.0.10
-lxml==4.6.3
+lxml==4.9.1
 macholib==1.11
 MarkupSafe==1.0
 multidict==4.4.2