Issue #3432489 add text about php file syncer being removed in 3.1.0

Closes #3432489

package_manager/src/Validator/RsyncValidator.php

@@ -72,7 +72,7 @@ final class RsyncValidator implements EventSubscriberInterface {
     if ($configured_syncer === 'php') {
       // Only status checks support warnings.
       if ($event instanceof StatusCheckEvent) {
-        $message = $this->t('You are currently using the PHP file syncer, which has known problems and is not stable. It is strongly recommended to switch back to the default <em>rsync</em> file syncer instead.');
+        $message = $this->t('You are currently using the PHP file syncer, which has known problems and is not stable. <strong>The PHP file syncer will be removed in Package Manager 3.1.0.</strong> Switch back to the default <em>rsync</em> file syncer to continue using Package Manager.');
 
         if (!$rsync_found) {
           $message = $this->t('@message <code>rsync</code> was not found on your system.', ['@message' => $message]);