fix(question): misplaced parenthesis

[btry]

triggers a PHP warning when adding a file question, breaking the refresh of the list of question in a section (if debug mode enabled)

[2025-05-13 14:12:34] glpiphplog.WARNING:   *** PHP Warning (2): Undefined array key "default_values" in /var/www/glpi/plugins/formcreator/inc/question.class.php at line 408
  Backtrace :
  src/CommonDBTM.php:1311                            PluginFormcreatorQuestion->prepareInputForAdd()
  plugins/formcreator/ajax/question_add.php:43       CommonDBTM->add()
  public/index.php:82                                require()

Changes description

Checklist

Please check if your PR fulfills the following specifications:

• Tests for the changes have been added
• Docs have been added/updated

References

Closes #N/A