MDL-86437 enrol_lti: Cast scoreGiven to float for LTI compliance

scoreGiven was being passed as a string (e.g. "8.0"), which caused
validation errors in some LMS implementations such as Rustici Engine.
According to the LTI specification, scoreGiven must be numeric if
present.

Co-authored-by: Jake Dallimore <[email protected]>

public/enrol/lti/classes/local/ltiadvantage/task/sync_tool_grades.php

@@ -122,6 +122,7 @@ class sync_tool_grades extends adhoc_task {
                         mtrace("Skipping - Invalid grade $mtracecontent.");
                         continue;
                     }
+                    $grade = floatval($grade); // Grade must be sent as a numeric value, not a string.
 
                     if (empty($grademax)) {
                         mtrace("Skipping - Invalid grademax $mtracecontent.");