Login and Registration: Use correct variable to display a single error message.

When the `wp_login_errors` filter is used to add an error message followed by an instructional message, the former was not displayed and the latter was errouneously displayed twice above the login form.

This commit ensures that the error message is displayed as expected.

Follow-up to [56654].

Props mapumba.
Fixes #59983.
Built from https://develop.svn.wordpress.org/trunk@57142


git-svn-id: http://core.svn.wordpress.org/trunk@56653 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.5-alpha-57141';
+$wp_version = '6.5-alpha-57142';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.

wp-login.php

@@ -257,7 +257,7 @@ function login_header( $title = 'Log In', $message = '', $wp_error = null ) {
 
 				$errors .= '</ul>';
 			} else {
-				$errors .= '<p>' . $error_message . '</p>';
+				$errors .= '<p>' . $error_list[0] . '</p>';
 			}
 
 			/**
@@ -265,9 +265,10 @@ function login_header( $title = 'Log In', $message = '', $wp_error = null ) {
 			 *
 			 * @since 2.1.0
 			 *
-			 * @param string $errors Login error message.
+			 * @param string $errors Login error messages.
 			 */
 			$errors = apply_filters( 'login_errors', $errors );
+
 			wp_admin_notice(
 				$errors,
 				array(
@@ -287,6 +288,7 @@ function login_header( $title = 'Log In', $message = '', $wp_error = null ) {
 			 * @param string $messages Login messages.
 			 */
 			$messages = apply_filters( 'login_messages', $messages );
+
 			wp_admin_notice(
 				$messages,
 				array(