connector_search_engine: store to_be_checked error

Before this change the error was visible only in the job
if not deleted.
This we can provide more info to the end user
w/o the need for a new field.
This info will be wiped on the next successful compute.

connector_search_engine/models/se_binding.py

@@ -204,6 +204,7 @@ def _recompute_json(self, force_export=False):
                         vals["date_modified"] = fields.Datetime.now()
                     if error:
                         vals["sync_state"] = "to_be_checked"
+                        vals["data"]["__error__"] = error
                     binding.write(vals)
         if validation_errors:
             result.append(