Fix get_statuses_! to handle non-200 status codes

[Gabriella439]

This is essentially the exact same fix as:

#1260

… except for get_statuses_! instead of get_checks_!

To provide some context (for both fixes), this is necessary in order to gracefully handle non-200 status codes. Before this fix the non-200 code path would set raw to an empty list, and fail with:

** (ArgumentError) the Access calls for keywords expect the key to be an atom, got: "statuses"
    (elixir 1.13.4) lib/access.ex:310: Access.get/3
    (bors 0.1.0) lib/github/github/server.ex:599: BorsNG.GitHub.Server.get_statuses_!/3
    (bors 0.1.0) lib/github/github/server.ex:430: BorsNG.GitHub.Server.do_handle_call/3
    (bors 0.1.0) lib/github/github/server.ex:965: BorsNG.GitHub.Server.use_token!/3
    (stdlib 3.17.2.1) gen_server.erl:721: :gen_server.try_handle_call/4
    (stdlib 3.17.2.1) gen_server.erl:750: :gen_server.handle_msg/6
    (stdlib 3.17.2.1) proc_lib.erl:226: :proc_lib.init_p_do_apply/3

… because it's trying to evaluate []["statuses"]. The fix is for raw to be an object of the correct shape so that the access succeeds.