check_model() uses rlang::arg_match()

[romainfrancois]

> mistral.ai::chat("hello", model = "fzzfz")
Error in `mistral.ai::chat()`:
! `model` must be one of "open-mistral-7b", "mistral-tiny-2312", "mistral-tiny", "open-mixtral-8x7b", "mistral-small-2312",
  "mistral-small", "mistral-small-2402", "mistral-small-latest", "mistral-medium-latest", "mistral-medium-2312", "mistral-medium",
  "mistral-large-latest", "mistral-large-2402", or "mistral-embed", not "fzzfz".
Run `rlang::last_trace()` to see where the error occurred.