Exercise: Fix issue limit of exercise itents - refs GH#3392

Author: lcubas

main/exercise/exercise.class.php

@@ -2257,10 +2257,10 @@ public function createForm($form, $type = 'full')
             $attempt_option[0] = get_lang('Infinite');
 
             $form->addElement(
-                'select',
+                'number',
                 'exerciseAttempts',
                 get_lang('ExerciseAttempts'),
-                $attempt_option,
+                null,
                 ['id' => 'exerciseAttempts']
             );