[8.x] Fix Http::withBody() not being sent

[deleugpn]

I'm currently building an Outgoing Webhook feature where users can select which HTTP Method they want to call and which URL. At some point in code, I have the following snippet:

        $response = Http::withHeaders($headers)
            ->withBody($body, 'application/json')
            ->send($webhook->method, $webhook->url);

However, this doesn't work because it doesn't match any condition in the send method, which then sends a request with an empty request body.

This pull request sends the pending body automatically if there is no instruction in $options on how to construct the request body.