Run Typeguard session only on the latest Python version (#764)

Author: staticdev

noxfile.py

@@ -172,7 +172,7 @@ def coverage(session: Session) -> None:
     session.run("coverage", *args)
 
 
-@session(python=python_versions)
+@session(python=python_versions[0])
 def typeguard(session: Session) -> None:
     """Runtime type checking using Typeguard."""
     session.install(".")