Bump lxml from 4.6.5 to 4.9.1 in /src/sonic-config-engine (#11366)

Bumps [lxml](https://github.com/lxml/lxml) from 4.6.5 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-4.6.5...lxml-4.9.1)

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

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src/sonic-config-engine/setup.py

@@ -7,7 +7,7 @@ from setuptools import setup
 dependencies = [
     'bitarray==1.5.3',
     'ipaddress==1.0.23',
-    'lxml==4.6.5',
+    'lxml==4.9.1',
     'netaddr==0.8.0',
     'pyyaml==5.4.1',
     'sonic-py-common',