Update dependency lxml to v6

Author: renovate[bot]

acceptance_tests/Pipfile

@@ -9,6 +9,6 @@ c2cwsgiutils = "==4.1.4"
 boltons = "==21.0.0"
 netifaces = "==0.11.0"
 requests = "==2.27.1"
-lxml = "==4.7.1"
+lxml = "==6.1.1"
 
 [dev-packages]