v3.1 license schema modified to describe url and identifier as mutually...

v3.1 license schema modified to describe url and identifier as mutually exclusive. Fixes #2975 (#2991)

schemas/v3.1/schema.yaml

@@ -105,11 +105,11 @@ $defs:
         format: uri
     required:
       - name
-    oneOf:
-      - required:
-        - identifier
-      - required:
-        - url
+    dependentSchemas:
+      identifier:
+        not:
+          required:
+            - url
     $ref: '#/$defs/specification-extensions'
     unevaluatedProperties: false