Fix superclass conditions on HasOpenApi (UVerb method cs (a ': as))

Unconditionally requesting `ToSchema a` etc means that we erroneously
demand `ToSchema NoContent`. Instead delegate to the `HasOpenApi`
instance for the related `Verb`, allowing the overlapping instances
for `NoContent` to be selected.

Author: JackKelly-Bellroy

CHANGELOG.md

@@ -1,6 +1,8 @@
 Unreleased
 ----------
 
+* The `HasOpenApi` instance that recurses through `UVerb` responses no
+  longer demands `ToSchema NoContent`.
 * Do not count `NoContent` as a body type if it appears in `Headers
   hdrs NoContent`.
 

src/Servant/OpenApi/Internal.hs

@@ -198,10 +198,7 @@ instance HasOpenApi (UVerb method cs '[]) where
 -- | @since <2.0.1.0>
 instance
   {-# OVERLAPPABLE #-}
-  ( ToSchema a,
-    HasStatus a,
-    AllAccept cs,
-    OpenApiMethod method,
+  ( HasOpenApi (Verb method (StatusOf a) cs a),
     HasOpenApi (UVerb method cs as)
   ) =>
   HasOpenApi (UVerb method cs (a ': as))