Merge pull request #314 from python-trio/dependabot/pip/lxml-4.6.4

Author: pquentin

test-requirements.txt

@@ -32,7 +32,7 @@ iniconfig==1.1.1
     # via pytest
 jinja2==3.0.2
     # via sphinx
-lxml==4.6.3
+lxml==4.6.4
     # via -r test-requirements.in
 markupsafe==2.0.1
     # via jinja2