Avoids potential error when alerts table is empty

Updates the Kernel to use the null-safe operator
when accessing the alerts_enabled setting. This prevents
a potential error if the settings object is null.

app/Console/Kernel.php

@@ -19,7 +19,7 @@ class Kernel extends ConsoleKernel
      */
     protected function schedule(Schedule $schedule)
     {
-        if(Setting::getSettings()->alerts_enabled === 1) {
+        if(Setting::getSettings()?->alerts_enabled === 1) {
             $schedule->command('snipeit:inventory-alerts')->daily();
             $schedule->command('snipeit:expiring-alerts')->daily();
             $schedule->command('snipeit:expected-checkin')->daily();