ref: use non-nullable .get() lookup instead of .first() (#75115)

this would always crash on line 263 if it were nullable

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src/sentry/api/endpoints/organization_events_trace.py

@@ -235,9 +235,9 @@ def load_span_serialized_performance_issues(self, light: bool) -> None:
             offender_span_ids = problem.evidence_data.get("offender_span_ids", [])
             for group_id in self.event["occurrence_to_issue_id"][problem.id]:
                 if group_id not in memoized_groups:
-                    memoized_groups[group_id] = Group.objects.filter(
+                    memoized_groups[group_id] = Group.objects.get(
                         id=group_id, project=self.event["project.id"]
-                    ).first()
+                    )
                 group = memoized_groups[group_id]
                 if event_span.get("span_id") in offender_span_ids:
                     start_timestamp = float(event_span["precise.start_ts"])