[#944582] Also check for files directory executable permission

core/includes/install.core.inc

core/includes/install.inc

core/lib/Drupal/Component/FileSystem/FileSystem.php

core/lib/Drupal/Core/File/FileSystem.php

core/lib/Drupal/Core/File/FileSystemInterface.php

core/lib/Drupal/Core/Updater/Updater.php

core/modules/config/src/Form/ConfigImportForm.php

core/modules/media/media.install

core/modules/migrate/src/Plugin/migrate/process/FileCopy.php

core/modules/system/src/Form/PerformanceForm.php

core/modules/system/system.install

core/modules/system/system.module