Posts, Post Types: Increment post_count option value only on multisite installations.

Avoid the `post_count` option to be created on single-site installations.

Follow-up to [52201].

Props dlh, henry.wright.
Fixes #54462.


git-svn-id: https://develop.svn.wordpress.org/trunk@52202 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/upgrade.php

@@ -250,7 +250,9 @@ if ( ! function_exists( 'wp_install_defaults' ) ) :
 			)
 		);
 
-		update_option( 'post_count', 1 );
+		if ( is_multisite() ) {
+			update_posts_count();
+		}
 
 		$wpdb->insert(
 			$wpdb->term_relationships,