move setting group metadata into assign_to_group

Author: lobsterkatie

src/sentry/event_manager.py

@@ -521,7 +521,7 @@ def save_error_events(
                 group_info = assign_event_to_group(
                     event=job["event"], job=job, metric_tags=metric_tags
                 )
-                job["groups"] = [group_info]
+
         except HashDiscarded as err:
             logger.info(
                 "event_manager.save.discard",
@@ -545,8 +545,6 @@ def save_error_events(
                 )
             return job["event"]
 
-        job["event"].group = group_info.group
-
         # store a reference to the group id to guarantee validation of isolation
         # XXX(markus): No clue what this does
         job["event"].data.bind_ref(job["event"])
@@ -1357,6 +1355,10 @@ def assign_event_to_group(event: Event, job: Job, metric_tags: MutableTags) -> O
             metric_tags=metric_tags,
         )
 
+    if group_info:
+        job["event"].group = group_info.group
+    job["groups"] = [group_info]
+
     return group_info