Fix example override of SchemaGenerator.get_schema()

Author: Mopsan

docs/api-guide/schemas.md

@@ -181,8 +181,8 @@ dictionary For example you might wish to add terms of service to the [top-level
 
 ```
 class TOSSchemaGenerator(SchemaGenerator):
-    def get_schema(self):
-        schema = super().get_schema()
+    def get_schema(self, *args, **kwargs):
+        schema = super().get_schema(*args, **kwargs)
         schema["info"]["termsOfService"] = "https://example.com/tos.html"
         return schema
 ```