Visible dependent quantification permitted in standalone deriving declarations

GHC 8.10.1 and later incorrectly allow VDQ in the type of a standalone deriving declaration:

{-# LANGUAGE DeriveAnyClass #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE StandaloneDeriving #-}
module Bug where

class C a
deriving instance forall a -> C (Maybe a)

Note that this only applies to standalone-derived instances. If you remove the deriving part of the last line, then GHC will reject it as expected.