Update noxfile.py

Author: chalmerlowe

noxfile.py

@@ -110,7 +110,7 @@ def lint(session):
 # and only 3.8).
 # As soon as that gets upgraded, we should be able to revert this session
 # to using the DEFAULT_PYTHON_VERSION.
-@nox.session(python="3.10")
+@nox.session(python="3.8")
 def blacken(session):
     """Run black. Format code to uniform standard."""
     session.install(BLACK_VERSION)