[9.x] Add assert methods for status code 400 and 408

[WendellAdriel]

This is adding two new assert methods for the response:

$this->assertBadRequest(); // Checks if status code is 400

$this->assertRequestTimeout(); // Checks if status code is 408

[taylorotwell]

Honestly I find it clearer to just assert on the actual status code. 😬

[WendellAdriel]

Got it! 😉

I just thought about adding that because in one of the projects I'm working on I was using some calls to assert these codes, but I understand 💪🏼

Thanks for taking some time to look into this either way! 🥳