try out a fix for this common code, that i will probably remove later as a special case

Author: wyattscarpenter

mypy/plugins/proper_plugin.py

@@ -12,6 +12,7 @@
 from typing import Callable
 
 from mypy.checker import TypeChecker
+from mypy.errorcodes import MISC
 from mypy.nodes import TypeInfo
 from mypy.plugin import FunctionContext, Plugin
 from mypy.subtypes import is_proper_subtype
@@ -72,6 +73,7 @@ def isinstance_proper_hook(ctx: FunctionContext) -> Type:
                 "If you pass on the original type"
                 " after the check, always use its unexpanded version",
                 ctx.context,
+                code=MISC,
             )
     return ctx.default_return_type