fix: [stix2 import] Setting single_event when parsing a bundle with…

… a single report/grouping, to avoid issues raised with multiple reports/groupings handling methods

misp_stix_converter/stix2misp/stix2_to_misp.py

@@ -656,6 +656,7 @@ def _parse_bundle_with_no_report(self):
         self._handle_unparsed_content()
 
     def _parse_bundle_with_single_report(self):
+        self.__single_event = True
         if hasattr(self, '_report') and self._report is not None:
             for report in self._report.values():
                 self.__misp_event = self._misp_event_from_report(report)