"example" and "examples" cannot appear together

This affects the places where examples are used: parameter, header, and media-type objects

for OAI#4598 and OAI#4776, ported from OAI#4912.

Author: karenetheridge

src/schemas/validation/schema.yaml

@@ -951,6 +951,10 @@ $defs:
         type: object
         additionalProperties:
           $ref: '#/$defs/example-or-reference'
+    not:
+      required:
+        - example
+        - examples
 
   map-of-strings:
     type: object