[6.x] Disable broadcast provider when broadcasting driver is null (#14471)

Author: jasonvarga

src/Providers/BroadcastServiceProvider.php

@@ -50,6 +50,10 @@ protected function variables()
 
     protected function enabled()
     {
+        if (config('broadcasting.default') === 'null') {
+            return false;
+        }
+
         return in_array(
             \Illuminate\Broadcasting\BroadcastServiceProvider::class,
             array_keys($this->app->getLoadedProviders())