Ignore 'unticked promoted constructors' in TypeErrors

The file is small enough that using unticked constructors should not be
error-prone

servant/src/Servant/API/TypeErrors.hs

@@ -4,6 +4,8 @@
 {-# LANGUAGE TypeOperators        #-}
 {-# LANGUAGE UndecidableInstances #-}
 
+{-# OPTIONS_GHC -fno-warn-unticked-promoted-constructors #-}
+
 -- | This module defines the error messages used in type-level errors.
 -- Type-level errors can signal non-existing instances, for instance when
 -- a combinator is not applied to the correct number of arguments.