[12.x] Fix relation auto loading with manually set relations (#55452)

Author: patrickweh

src/Illuminate/Database/Eloquent/Concerns/HasRelationships.php

@@ -184,7 +184,7 @@ protected function propagateRelationAutoloadCallbackToRelation($key, $models, $c
 
         foreach ($models as $model) {
             // Check if relation autoload contexts are different to avoid circular relation autoload...
-            if (is_null($context) || $context !== $model) {
+            if ((is_null($context) || $context !== $model) && is_object($model) && method_exists($model, 'autoloadRelationsUsing')) {
                 $model->autoloadRelationsUsing($callback, $context);
             }
         }