Fix add events.id to GROUP BY to resolve PostgreSQL aggregation error

Signed-off-by: Asai Neko <sugar@sne.moe>

data/stats.go

@@ -58,7 +58,7 @@ func (self *GlobalStats) EventJoinCheckinCounts(ctx context.Context) (*[]EventSt
 			SUM(CASE WHEN attendances.checkin_at > ? THEN 1 ELSE 0 END) AS checkin_count
 		`, zero).
 		Joins("LEFT JOIN attendances ON attendances.event_id = events.event_id").
-		Group("events.event_id, events.name").
+		Group("events.id, events.event_id, events.name").
 		Order("events.id ASC").
 		Scan(&results).Error