[ticket/17366] Remember confirm code if recaptcha v3 is solved

PHPBB-17366

phpBB/phpbb/captcha/plugins/recaptcha_v3.php

@@ -359,6 +359,7 @@ class recaptcha_v3 extends captcha_abstract
 		if ($result->isSuccess())
 		{
 			$this->solved = true;
+			$this->confirm_code = $this->code;
 
 			return false;
 		}