Accessibility: Login and Registration: Add a `role="main"` landmark to the container div in `wp-signup.php`.

Props SteelWagstaff, audrasjb.
Fixes #48657.
Built from https://develop.svn.wordpress.org/trunk@47075


git-svn-id: http://core.svn.wordpress.org/trunk@46875 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.4-alpha-47074';
+$wp_version = '5.4-alpha-47075';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.

wp-signup.php

@@ -86,7 +86,7 @@ get_header( 'wp-signup' );
 do_action( 'before_signup_form' );
 ?>
 <div id="signup-content" class="widecolumn">
-<div class="mu_register wp-signup-container">
+<div class="mu_register wp-signup-container" role="main">
 <?php
 /**
  * Generates and displays the Signup and Create Site forms