Merge pull request #31859 from max65482/fix_group_share

Fix: Birthday calendar issue with shared calendars

apps/dav/lib/DAV/Sharing/Backend.php

@@ -184,7 +184,7 @@ class Backend {
 				'status' => 1,
 				'readOnly' => (int) $row['access'] === self::ACCESS_READ,
 				'{http://owncloud.org/ns}principal' => (string)$row['principaluri'],
-				'{http://owncloud.org/ns}group-share' => is_null($p)
+				'{http://owncloud.org/ns}group-share' => isset($p['uri']) ? str_starts_with($p['uri'], 'principals/groups') : false
 			];
 		}