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

src/Updater.php

@@ -19,6 +19,7 @@ use PhpTuf\ComposerStager\Domain\CleanerInterface;
 use PhpTuf\ComposerStager\Domain\CommitterInterface;
 use PhpTuf\ComposerStager\Domain\StagerInterface;
 use Symfony\Component\EventDispatcher\EventDispatcherInterface;
+use Symfony\Component\Filesystem\Filesystem as SymfonyFilesystem;
 
 /**
  * Defines a service to perform updates.
@@ -277,8 +278,10 @@ class Updater {
    * Cleans the current update.
    */
   public function clean(): void {
-    if (is_dir($this->getStageDirectory())) {
-      $this->cleaner->clean($this->getStageDirectory());
+    $dir = $this->getStageDirectory();
+    if (is_dir($dir)) {
+      (new SymfonyFilesystem())->chmod($dir, 0777);
+      $this->cleaner->clean($dir);
     }
     $this->state->delete(static::STATE_KEY);
   }