Twenty Twenty-One: Fix the nesting of the `main` element.

The `main` element must not appear as a descendant of the `section` element. Correct markup is the first requirement to make user agents and assistive technologies work properly.

Changes the `<section>` element that was wrapping the `<main>` element to a `<div>`.

Follow-up to [45942] for Twenty Nineteen.

Props albertomake, poena.
Fixes #51944.
}}}
Built from https://develop.svn.wordpress.org/trunk@49759


git-svn-id: http://core.svn.wordpress.org/trunk@49482 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-content/themes/twentytwentyone/footer.php

@@ -13,7 +13,7 @@
 
 ?>
 			</main><!-- #main -->
-		</section><!-- #primary -->
+		</div><!-- #primary -->
 	</div><!-- #content -->
 
 	<?php get_template_part( 'template-parts/footer/footer-widgets' ); ?>

wp-content/themes/twentytwentyone/header.php

@@ -28,5 +28,5 @@
 	<?php get_template_part( 'template-parts/header/site-header' ); ?>
 
 	<div id="content" class="site-content">
-		<section id="primary" class="content-area">
+		<div id="primary" class="content-area">
 			<main id="main" class="site-main" role="main">

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.7-alpha-49758';
+$wp_version = '5.7-alpha-49759';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.