Bundled Themes: Twenty Twenty submenu items disappear underneath the Cover block.

Fixes the submenu issue by raising the z-index value of the site-header from 1 to 2.

Props kjellr, JavierCasares.
Fixes #49322.
Built from https://develop.svn.wordpress.org/trunk@47609


git-svn-id: http://core.svn.wordpress.org/trunk@47384 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-content/themes/twentytwenty/style-rtl.css

@@ -5598,7 +5598,7 @@ a.to-the-top > * {
 	/* Site Header --------------------------- */
 
 	#site-header {
-		z-index: 1;
+		z-index: 2;
 	}
 
 	.header-inner {

wp-content/themes/twentytwenty/style.css

@@ -5660,7 +5660,7 @@ a.to-the-top > * {
 	/* Site Header --------------------------- */
 
 	#site-header {
-		z-index: 1;
+		z-index: 2;
 	}
 
 	.header-inner {

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.5-alpha-47608';
+$wp_version = '5.5-alpha-47609';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.