fix(caldav): don't reuse query builder objects

Signed-off-by: Anna Larch <anna@nextcloud.com>

Author: miaulalala

apps/dav/lib/CalDAV/CalDavBackend.php

@@ -3085,11 +3085,13 @@ public function purgeAllCachedEventsForSubscription($subscriptionId) {
 				->andWhere($query->expr()->eq('calendartype', $query->createNamedParameter(self::CALENDAR_TYPE_SUBSCRIPTION)))
 				->executeStatement();
 
+			$query = $this->db->getQueryBuilder();
 			$query->delete('calendarchanges')
 				->where($query->expr()->eq('calendarid', $query->createNamedParameter($subscriptionId)))
 				->andWhere($query->expr()->eq('calendartype', $query->createNamedParameter(self::CALENDAR_TYPE_SUBSCRIPTION)))
 				->executeStatement();
 
+			$query = $this->db->getQueryBuilder();
 			$query->delete($this->dbObjectPropertiesTable)
 				->where($query->expr()->eq('calendarid', $query->createNamedParameter($subscriptionId)))
 				->andWhere($query->expr()->eq('calendartype', $query->createNamedParameter(self::CALENDAR_TYPE_SUBSCRIPTION)))