Issue #3231992: Make the staged sites/default writable before cleaning

src/ComposerStager/Cleaner.php

@@ -58,7 +58,7 @@ class Cleaner implements CleanerInterface {
    * {@inheritdoc}
    */
   public function clean(string $stagingDir, ?ProcessOutputCallbackInterface $callback = NULL, ?int $timeout = 120): void {
-    // Ensure that the staged site directory is writable.
+    // Ensure that the staged site directory is writable so we can delete it.
     $site_dir = implode(DIRECTORY_SEPARATOR, [
       $stagingDir,
       $this->pathLocator->getWebRoot() ?: '.',