Issue #3227940: Ensure 8.x-2.x branch tests pass on Drupalci

tests/src/Kernel/UpdaterTest.php

@@ -126,9 +126,7 @@ class TestUpdater extends Updater {
    * {@inheritdoc}
    */
   public function getStageDirectory(): string {
-    /** @var \Drupal\Core\File\FileSystemInterface $fs */
-    $fs = \Drupal::service('file_system');
-    return $fs->getTempDirectory() . "/" . microtime();
+    return $this->fileSystem->realpath('public://') . microtime();
   }
 
 }