test: update test for mountpoint numeric storage id

Signed-off-by: Robin Appelman <robin@icewind.nl>

tests/lib/Files/Config/UserMountCacheTest.php

@@ -101,6 +101,8 @@ class UserMountCacheTest extends TestCase {
 		$cache->expects($this->any())
 			->method('getId')
 			->willReturn($rootId);
+		$cache->method('getNumericStorageId')
+			->willReturn($storageId);
 
 		$storage = $this->getMockBuilder('\OC\Files\Storage\Storage')
 			->disableOriginalConstructor()