Grade item: MDL-21161 timemodified never gets set on calculated gradebook columns

lib/grade/grade_item.php

@@ -1815,6 +1815,7 @@ class grade_item extends grade_object {
 
         // update in db if changed
         if (grade_floats_different($grade->finalgrade, $oldfinalgrade)) {
+            $grade->timemodified = time();
             $grade->update('compute');
         }