Merge pull request #49679 from nextcloud/backport/49677/stable29

[stable29] fix(db): Create the systag_by_objectid index for new installations

core/Migrations/Version13000Date20170718121200.php

@@ -756,6 +756,8 @@ public function changeSchema(IOutput $output, \Closure $schemaClosure, array $op
 			$table->setPrimaryKey(['objecttype', 'objectid', 'systemtagid'], 'som_pk');
 			//			$table->addUniqueIndex(['objecttype', 'objectid', 'systemtagid'], 'mapping');
 			$table->addIndex(['systemtagid', 'objecttype'], 'systag_by_tagid');
+			// systag_by_objectid was added later and might be missing in older deployments
+			$table->addIndex(['objectid'], 'systag_by_objectid');
 		}
 
 		if (!$schema->hasTable('systemtag_group')) {