fix: [stix2 import] Avoiding issue with getattr which isn't able to…

… check whether a `__` prefixed variable exists or not

misp_stix_converter/stix2misp/stix2_to_misp.py

@@ -315,7 +315,7 @@ def course_of_action_parser(self) -> _COURSE_OF_ACTION_PARSER_TYPING:
 
     @property
     def event_tags(self) -> list:
-        return getattr(self, '__event_tags', {})
+        return self.__event_tags
 
     @property
     def generic_info_field(self) -> str: