fix(dav): undeclared `$cache` property

Signed-off-by: John Molakvoæ <skjnldsv@protonmail.com>

apps/dav/tests/unit/CalDAV/Status/StatusServiceTest.php

@@ -49,6 +49,7 @@ class StatusServiceTest extends TestCase {
 	private IAvailabilityCoordinator|MockObject $availabilityCoordinator;
 	private ICacheFactory|MockObject $cacheFactory;
 	private LoggerInterface|MockObject $logger;
+	private ICache|MockObject $cache;
 	private StatusService $service;
 
 	protected function setUp(): void {