loaders: fix flask 2 compatibility

Author: NRodriguezcuellar

invenio_records_rest/loaders/marshmallow.py

@@ -75,7 +75,7 @@ def __next__(self):
         """Get next file item."""
         return next(self._it)
 
-    def get_body(self, environ=None):
+    def get_body(self, environ=None, scope=None):
         """Get the request body."""
         body = dict(
             status=self.code,