Site Health: Use `WP_Theme::parent()` in the inactive themes test as a more reliable check that the parent theme exists.

This is also more consistent with the other instances of directly referencing `WP_Theme::parent()` properties or methods in core.

Props mukesh27, juanlopez4691, davidbaumwald, afragen, SergeyBiryukov.
Fixes #49934.
Built from https://develop.svn.wordpress.org/trunk@47815


git-svn-id: http://core.svn.wordpress.org/trunk@47591 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/includes/class-wp-site-health.php

@@ -596,7 +596,7 @@ class WP_Site_Health {
 		if ( $has_unused_themes && $show_unused_themes && ! is_multisite() ) {
 
 			// This is a child theme, so we want to be a bit more explicit in our messages.
-			if ( is_child_theme() ) {
+			if ( $active_theme->parent() ) {
 				// Recommend removing inactive themes, except a default theme, your current one, and the parent theme.
 				$result['status'] = 'recommended';
 

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.5-alpha-47814';
+$wp_version = '5.5-alpha-47815';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.