fix: check instance of storage using helper function

instanceof cannot be used to check the instance of a storage, doing so
breaks the check in certain cases. In this case, enabling the
`files_accesscontrol` app breaks the check.

Signed-off-by: Salvatore Martire <[email protected]>

Author: salmart-dev

apps/dav/lib/Connector/Sabre/Directory.php

@@ -181,7 +181,7 @@ public function getChild($name, $info = null, ?IRequest $request = null, ?IL10N
 		// If we are, then only PUT and MKCOL are allowed (see plugin)
 		// so we are safe to return the directory without a risk of
 		// leaking files and folders structure.
-		if ($storage instanceof PublicShareWrapper) {
+		if ($storage->instanceOfStorage(PublicShareWrapper::class)) {
 			$share = $storage->getShare();
 			$allowDirectory = ($share->getPermissions() & Constants::PERMISSION_READ) !== Constants::PERMISSION_READ;
 		}

apps/dav/tests/unit/Connector/Sabre/DirectoryTest.php

@@ -21,6 +21,7 @@
 use OCP\Files\ForbiddenException;
 use OCP\Files\InvalidPathException;
 use OCP\Files\Mount\IMountPoint;
+use OCP\Files\Storage\IStorage;
 use OCP\Files\StorageNotAvailableException;
 use PHPUnit\Framework\MockObject\MockObject;
 use Test\Traits\UserTrait;
@@ -61,12 +62,16 @@ class DirectoryTest extends \Test\TestCase {
 
 	private View&MockObject $view;
 	private FileInfo&MockObject $info;
+	private IStorage&MockObject $storage;
 
 	protected function setUp(): void {
 		parent::setUp();
 
 		$this->view = $this->createMock(View::class);
 		$this->info = $this->createMock(FileInfo::class);
+		$this->storage = $this->createMock(IStorage::class);
+		$this->info->method('getStorage')
+			->willReturn($this->storage);
 		$this->info->method('isReadable')
 			->willReturn(true);
 		$this->info->method('getType')