chore(deps): bump lxml from 4.6.2 to 4.9.1

Bumps [lxml](https://github.com/lxml/lxml) from 4.6.2 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-4.6.2...lxml-4.9.1)

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

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

setup.py

@@ -59,7 +59,7 @@
     "keyring==17.1.1",
     "keystoneauth1==3.11.2",
     "libsass==0.16.1",
-    "lxml==4.6.2",
+    "lxml==4.9.1",
     "Mako==1.0.7",
     "Markdown==2.6.11",
     "MarkupSafe==1.1.0",