Merge pull request #1124 from python-trio/dependabot/pip/isort-4.3.21

Author: dependabot-preview[bot]

test-requirements.txt

@@ -22,7 +22,7 @@ immutables==0.9
 importlib-metadata==0.18  # via pluggy, pytest
 ipython-genutils==0.2.0   # via traitlets
 ipython==7.5.0
-isort==4.3.20             # via pylint
+isort==4.3.21             # via pylint
 jedi==0.13.3
 lazy-object-proxy==1.4.1  # via astroid
 mccabe==0.6.1             # via flake8, pylint