Fix up basepython for local runs.

Author: ubernostrum

tox.ini

@@ -137,6 +137,7 @@ commands =
 # flake8 finds any problems.
 [testenv:flake8]
 description = Lint code with flake8.
+basepython = python3.9
 changedir = {toxinidir}
 deps = flake8
 commands =
@@ -146,6 +147,7 @@ commands =
 # any problems are found.
 [testenv:isort]
 description = Lint imports with isort.
+basepython = python3.9
 changedir = {toxinidir}
 deps = isort
 commands =