Add a required check for exam lab percentage

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src/main/resources/templates/lab/create.html

@@ -330,10 +330,12 @@
             $('#inputExamLab').change(function() {
                 if ($('#inputExamLab').is(':checked')) {
                     $('#percentageExamLab').prop('disabled', false)
+                            .attr('required', true);
                     $('#inputTimeIntervals').prop('checked', true);
                     toggleTimeIntervals();
                 } else {
                     $('#percentageExamLab').prop('disabled', true)
+                            .removeAttr('required', false);
                 }
             });
         });