Add {pkgsMusl,pkgsStatic}.stdenv to build on hydra (#89425)

* Add pkgsMusl.stdenv to block nixpkgs channel

* Don’t include i686-linux for pkgs{Musl,Static}

musl bootstrapping is unavailable for i686-linux right now. so we can
just exclude it from hydra.

Co-authored-by: Matthew Bauer <mjbauer95@gmail.com>