pytest.ini: Treat warnings as errors

Author: t-b

pytest.ini

@@ -6,6 +6,7 @@ markers =
     requires_inhouse_data: require inhouse data
 
 filterwarnings =
+    error
     ignore:add_child is deprecated. Set the parent attribute instead.:DeprecationWarning
     ignore::marshmallow.warnings.RemovedInMarshmallow4Warning
     ignore::marshmallow.warnings.ChangedInMarshmallow4Warning