Issue #2951558 by Florent Jousseaume: Fix requirements check when using symlinks.

file_browser.install

@@ -77,7 +77,8 @@ https://github.com/desandro/masonry/releases and place it in /libraries'
   }
 
   // Prevent installation if the webserver cannot write to "public://" .
-  if (!\Drupal::isConfigSyncing() && !is_writable('public://')) {
+  $public_path = \Drupal::service('file_system')->realpath('public://');
+  if (!\Drupal::isConfigSyncing() && !is_writable($public_path)) {
     $requirements['public_files_not_writable'] = [
       'title' => t('Public files directory not writable'),
       'description' => t('The webserver needs to be able to write to the public files directory (public://). Please check your server configuration and try again.'),