Upgrade/Install: Differentiate en_US version strings from localized ones.

Adds a condition to `$version_string` to determine whether the Core update is the original en_US package, or a localized one.

This change fixes an issue where these packages were not differentiated and duplicate messages were displayed.

Props Presskopp, benjamingosset.
Fixes #53710.

Built from https://develop.svn.wordpress.org/trunk@52197


git-svn-id: http://core.svn.wordpress.org/trunk@51789 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/update-core.php

@@ -48,6 +48,8 @@ function list_core_update( $update ) {
 			// If the only available update is a partial builds, it doesn't need a language-specific version string.
 			$version_string = $update->current;
 		}
+	} elseif ( 'en_US' === $update->locale && 'en_US' !== get_locale() ) {
+		$version_string = sprintf( '%s–%s', $update->current, $update->locale );
 	}
 
 	$current = false;