feat(escalating-issues): Add GroupForecast to Group related models (#46205)

## Objective:

This array is used for group deletion. 

Related comment:
https://github.com/getsentry/sentry/pull/45971#discussion_r1143683237

src/sentry/deletions/defaults/group.py

@@ -31,6 +31,7 @@ DIRECT_GROUP_RELATED_MODELS = (
     models.GroupSubscription,
     models.GroupHistory,
     models.RuleFireHistory,
+    models.GroupForecast,
 )
 
 _GROUP_RELATED_MODELS = DIRECT_GROUP_RELATED_MODELS + (