MDL-79324 quiz: Don't show "Back" button in secure layout.

public/mod/quiz/classes/output/renderer.php

@@ -534,6 +534,10 @@ class renderer extends plugin_renderer_base {
      */
     public function during_attempt_tertiary_nav($quizviewurl): string {
         $output = '';
+        if ($this->page->pagelayout === 'secure') {
+            // Do not show the back button in the secure layout on quiz pages.
+            return $output;
+        }
         $output .= html_writer::start_div('tertiary-navigation');
         $output .= html_writer::start_div('row');
         $output .= html_writer::start_div('navitem');

public/mod/quiz/tests/behat/attempt_secure_layout.feature

@@ -79,3 +79,4 @@ Feature: Attempt a quiz in secure layout
     But I should not see "Quiz 1 description"
     And I should not see "Opened:"
     And I should not see "Closes:"
+    And I should not see "Back"