MDL-49826 gradereport_singleview: fix permission check

Users with capability 'moodle/grade:edit' should be able to edit grade values
- 'moodle/grade:manage' is not needed, as grade items are not being changed.

grade/report/singleview/lib.php

@@ -52,7 +52,7 @@ class gradereport_singleview extends grade_report {
      * @return array List of warnings
      */
     public function process_data($data) {
-        if (has_capability('moodle/grade:manage', $this->context)) {
+        if (has_capability('moodle/grade:edit', $this->context)) {
             return $this->screen->process($data);
         }
     }