Raise ValueError from assigned variable

Co-authored-by: Henry Schreiner <[email protected]>

nox/sessions.py

@@ -380,8 +380,8 @@ def run(
             raise ValueError("At least one argument required to run().")
 
         if len(args) == 1 and isinstance(args[0], (list, tuple)):
-            raise ValueError("First argument to `session.run` is a list. "
-                               "Did you mean to use `session.run(*args)`?")
+            msg = "First argument to `session.run` is a list. Did you mean to use `session.run(*args)`?"
+            raise ValueError(msg)
 
         if self._runner.global_config.install_only:
             logger.info(f"Skipping {args[0]} run, as --install-only is set.")