Merge pull request #54652 from nextcloud/backport/54650/stable31

[stable31] fix(carddav): IAddressBook::getKey() should return a string

Author: AndyScherzinger

apps/dav/lib/CardDAV/AddressBookImpl.php

@@ -41,7 +41,7 @@ public function __construct(
 	 * @since 5.0.0
 	 */
 	public function getKey() {
-		return $this->addressBookInfo['id'];
+		return (string)$this->addressBookInfo['id'];
 	}
 
 	/**

apps/dav/tests/unit/CardDAV/AddressBookImplTest.php

@@ -67,7 +67,8 @@ protected function setUp(): void {
 	}
 
 	public function testGetKey(): void {
-		$this->assertSame($this->addressBookInfo['id'],
+		$this->assertIsString($this->addressBookImpl->getKey());
+		$this->assertSame((string)$this->addressBookInfo['id'],
 			$this->addressBookImpl->getKey());
 	}