fix: update stock validation to be conditionally required based on request method

app/Http/Requests/Admin/Master/ProductRequest.php

@@ -40,7 +40,7 @@ public function rules(): array
             'images.*' => ['image', 'max:5120'],
             'delete_image_ids' => ['nullable', 'array'],
             'delete_image_ids.*' => ['integer'],
-            'stock' => ['required', 'integer', 'min:0'],
+            'stock' => [Rule::requiredIf($this->isMethod('post')), 'integer', 'min:0'],
         ];
     }
 }