Resolve #3408488 "Make unknownpathexcluder accept"

Closes #3408488

package_manager/src/PathExcluder/UnknownPathExcluder.php

@@ -102,20 +102,19 @@ final class UnknownPathExcluder implements EventSubscriberInterface {
     // glob() flags aren't supported on all systems. We also can't use
     // \Drupal\Core\File\FileSystemInterface::scanDirectory(), because it
     // unconditionally ignores hidden files and directories.
-    $paths_in_project_root = [];
+    $unknown_paths = [];
     $handle = opendir($project_root);
     if (empty($handle)) {
       throw new \RuntimeException("Could not scan for files in the project root.");
     }
     while ($entry = readdir($handle)) {
-      if ($entry === '.' || $entry === '..') {
+      if ($entry === '.' || $entry === '..' || in_array($entry, $known_paths, TRUE)) {
         continue;
       }
-      $paths_in_project_root[] = $entry;
+      $unknown_paths[] = $entry;
     }
     closedir($handle);
 
-    $unknown_paths = array_diff($paths_in_project_root, $known_paths);
     $event->addPathsRelativeToProjectRoot($unknown_paths);
   }