/usr/share/php/sabre21/Sabre/DAVACL/ is in php-sabre-dav-2.1 2.1.10-1ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/php/sabre21/Sabre/DAVACL/AbstractPrincipalCollection.php
/usr/share/php/sabre21/Sabre/DAVACL/Exception/
/usr/share/php/sabre21/Sabre/DAVACL/Exception/AceConflict.php
/usr/share/php/sabre21/Sabre/DAVACL/Exception/NeedPrivileges.php
/usr/share/php/sabre21/Sabre/DAVACL/Exception/NoAbstract.php
/usr/share/php/sabre21/Sabre/DAVACL/Exception/NotRecognizedPrincipal.php
/usr/share/php/sabre21/Sabre/DAVACL/Exception/NotSupportedPrivilege.php
/usr/share/php/sabre21/Sabre/DAVACL/IACL.php
/usr/share/php/sabre21/Sabre/DAVACL/IPrincipal.php
/usr/share/php/sabre21/Sabre/DAVACL/IPrincipalCollection.php
/usr/share/php/sabre21/Sabre/DAVACL/Plugin.php
/usr/share/php/sabre21/Sabre/DAVACL/Principal.php
/usr/share/php/sabre21/Sabre/DAVACL/PrincipalBackend/
/usr/share/php/sabre21/Sabre/DAVACL/PrincipalBackend/AbstractBackend.php
/usr/share/php/sabre21/Sabre/DAVACL/PrincipalBackend/BackendInterface.php
/usr/share/php/sabre21/Sabre/DAVACL/PrincipalBackend/PDO.php
/usr/share/php/sabre21/Sabre/DAVACL/PrincipalCollection.php
/usr/share/php/sabre21/Sabre/DAVACL/Property/
/usr/share/php/sabre21/Sabre/DAVACL/Property/Acl.php
/usr/share/php/sabre21/Sabre/DAVACL/Property/AclRestrictions.php
/usr/share/php/sabre21/Sabre/DAVACL/Property/CurrentUserPrivilegeSet.php
/usr/share/php/sabre21/Sabre/DAVACL/Property/Principal.php
/usr/share/php/sabre21/Sabre/DAVACL/Property/SupportedPrivilegeSet.php