Merge pull request #1954 from python-trio/dependabot/pip/astroid-2.5.3

Author: dependabot-preview[bot]

test-requirements.txt

@@ -8,7 +8,7 @@ appdirs==1.4.4
     # via black
 astor==0.8.1
     # via -r test-requirements.in
-astroid==2.5.1
+astroid==2.5.3
     # via pylint
 async-generator==1.10
     # via -r test-requirements.in