MDL-75947 ltiservice_gradebookservices: use score->timestamp as dateg…

…raded

If this is not passed in to grade_update(), then it's not passed on to
update_raw_grade(), resulting in time() being used instead, which isn't
correct. The grade timemodified value should be set to the timestamp
provided by the tool in the score post JSON, not the time of the score
post itself.

mod/lti/service/gradebookservices/classes/local/service/gradebookservices.php

@@ -541,6 +541,7 @@ public function save_grade_item($gradeitem, $score, $userid) {
             $grade->feedbackformat = $feedbackformat;
             $grade->feedback = $feedback;
             $grade->rawgrade = $finalgrade;
+            $grade->dategraded = $timemodified;
             $status = grade_update($source, $gradeitem->courseid,
                 $gradeitem->itemtype, $gradeitem->itemmodule,
                 $gradeitem->iteminstance, $gradeitem->itemnumber, $grade);