style(mypy): enforce warn_return_any check

Author: Lee-W

setup.cfg

@@ -12,7 +12,7 @@ ignore_missing_imports = true
 disallow_untyped_decorators = true
 # disallow_any_generics = True
 disallow_subclassing_any = true
-# warn_return_any = True
+warn_return_any = True
 warn_redundant_casts = true
 warn_unused_ignores = true
 warn_unused_configs = true