workflows: look for existence of json content with private attribute (#36515)

wcs/forms/workflows.py

@@ -57,7 +57,7 @@ class HookDirectory(Directory):
             else:
                 raise errors.AccessForbiddenError('insufficient roles')
 
-        if hasattr(get_request(), 'json'):
+        if hasattr(get_request(), '_json'):
             workflow_data = {self.trigger.identifier: get_request().json}
             self.formdata.update_workflow_data(workflow_data)
             self.formdata.store()