fix: raises exception when a 404 is encountered

the api raises a 404 if an object isn't found when trying to get
particular objects, since making the _get method generic so it's
reusable across various other objects, it was missing handling the 404
exception, this covers that.

Note that the list methods will probably ignore this but it's as valid
to include the exception handling in the fetch

gallagher/cc/core.py

@@ -383,6 +383,8 @@ async def _get(
 
                     return parsed_obj
 
+                elif response.status_code == HTTPStatus.NOT_FOUND:
+                    raise NotFoundException()
                 elif response.status_code == HTTPStatus.FORBIDDEN:
                     raise UnlicensedFeatureException()
                 elif response.status_code == HTTPStatus.UNAUTHORIZED: