Do not send empty JSON object as body with GET requests

[Stranger6667]

By default, schemathesis will generate an empty dictionary in Case arguments if there is nothing, but requests will serialize it to {} for body and will send with the requests. In some cases, it is possible to get 400, not from the application, but form some intermediate parties:

Your client has issued a malformed or illegal request

which is not what we want.
In general, it is not clear, what is needed - no body or empty JSON object as a body. It should be fixed

[Stranger6667]

In tests, we didn't check this and many tests use data generation from schemas with such issues