Updated files with 'repo_helper'.

Author: repo-helper[bot]

.github/workflows/flake8.yml

@@ -16,7 +16,7 @@ permissions:
 jobs:
   Run:
     name: "Flake8"
-    runs-on: "ubuntu-18.04"
+    runs-on: "ubuntu-20.04"
 
     steps:
       - name: Checkout 🛎️

tox.ini

@@ -30,6 +30,7 @@ qa = mypy, lint
 setenv =
     PYTHONDEVMODE=1
     PIP_DISABLE_PIP_VERSION_CHECK=1
+    SETUPTOOLS_USE_DISTUTILS=stdlib
 deps = importcheck>=0.1.0
 commands =
     python --version