MDL-57597 competency: Fix serving of prior learning evidence files

For security reasons, all files submitted by students must be disposed
as attachments, not inline contents.

competency/lib.php

@@ -288,6 +288,7 @@ function core_competency_pluginfile($course, $cm, $context, $filearea, $args, $f
     if ($filearea == 'userevidence' && $context->contextlevel == CONTEXT_USER) {
         if (user_evidence::can_read_user($context->instanceid)) {
             $file = $fs->get_file($context->id, 'core_competency', $filearea, $itemid, $filepath, $filename);
+            $forcedownload = true;
         }
     }