HomeworkFolder: use folder-edit icons instead of folder-lock icons, fixes #4691

Closes #4691

Merge request studip/studip!3591

lib/filesystem/HomeworkFolder.php

@@ -54,8 +54,8 @@ class HomeworkFolder extends PermissionEnabledFolder
     public function getIcon($role = Icon::DEFAULT_ROLE)
     {
         $shape = $this->is_empty
-              ? 'folder-lock-empty'
-              : 'folder-lock-full';
+              ? 'folder-edit-empty'
+              : 'folder-edit-full';
         return Icon::create($shape, $role);
     }