MDL-81520 core: Fix test finality

lib/tests/accesslib_test.php

@@ -30,7 +30,18 @@ defined('MOODLE_INTERNAL') || die();
  *
  * Note: execution may take many minutes especially on slower servers.
  */
-class accesslib_test extends advanced_testcase {
+final class accesslib_test extends advanced_testcase {
+
+    /**
+     * Setup.
+     */
+    protected function setUp(): void {
+        parent::setUp();
+        $this->resetAfterTest();
+        // Turn off the course welcome message, so we can easily test other messages.
+        set_config('sendcoursewelcomemessage', 0, 'enrol_manual');
+    }
+
     /**
      * Verify comparison of context instances in phpunit asserts.
      */