Fix adjustInventoryLevel response

[BrandonKerr]

When calling $this->shopify->adjustInventoryLevel(...), I would get this error:

TypeError

Signifly\Shopify\REST\Resources\ApiResource::__construct(): Argument #1 ($attributes) must be of type array, null given, called in /app/musora-web-platform/vendor/signifly/laravel-shopify/src/REST/Actions/ManagesInventory.php on line 56

After looking into the response in the adjustInventoryLevel function, I found that there was no "inventory_level" value, and after a few trials, found that returning the $response->json() as the first parameter for the ApiResource seemed to create the expected results, based on looking at some other actions' responses.

I expect this change (if it's accepted) should be applied to all other functions in this class that are returning new ApiResource($response['inventory_level'], $this), but since I haven't yet had a need to call the other functions, I haven't tested these cases and left them for now.