[python-experimental] adds test verifying inheriting from multiple AnyType classes (#13358)

* Adds test_additional_properties_validator

* Updates test

* Reverts file

modules/openapi-generator/src/test/resources/3_0/python-experimental/petstore-with-fake-endpoints-models-for-testing-with-http-signature.yaml

@@ -2905,4 +2905,15 @@ components:
           type: string
           enum:
             - move
-            - copy
+            - copy
+    AdditionalPropertiesValidator:
+      type: object
+      allOf:
+        - type: object
+          additionalProperties: true
+        - type: object
+          additionalProperties:
+            minLength: 3
+        - type: object
+          additionalProperties:
+            maxLength: 5