The "unstable" alert in OCaml 5.0 is enabled by default in merlin

[kit-ty-kate]

The Warnings module in OCaml 5.0 doesn't correspond to what's in this module upstream:

merlin/src/ocaml/utils/warnings.ml

Line 507 in c447386

alerts = (Std.String.Set.empty, false); (* all enabled *)

Upstream, the unstable alert is disabled by default:

https://github.com/ocaml/ocaml/blob/34cf5aafcedc2f7895c7f5f0ac27c7e58e4f4adf/utils/warnings.ml#L861