Index: src/wp-admin/includes/class-wp-site-health.php
===================================================================
--- src/wp-admin/includes/class-wp-site-health.php	(revision 45305)
+++ src/wp-admin/includes/class-wp-site-health.php	(working copy)
@@ -355,7 +355,7 @@
 					sprintf(
 						/* translators: %d: The number of active plugins. */
 						_n(
-							'Your site has %d active plugin, and they are all up to date.',
+							'Your site has %d active plugin, and it is up to date.',
 							'Your site has %d active plugins, and they are all up to date.',
 							$plugins_active
 						),