Issue #3328234: Improve test DX *and* confidence: assert VFS state

package_manager/tests/src/Kernel/StageOwnershipTest.php

@@ -285,7 +285,7 @@ class StageOwnershipTest extends PackageManagerKernelTestBase {
     // Write-protect the stage directory, which should prevent files in it from
     // being deleted.
     $dir = $stage->getStageDirectory();
-    chmod($dir, 0400);
+    chmod($dir, 0500);
     $this->assertDirectoryIsNotWritable($dir);
 
     $logger = new TestLogger();