FIx the CI

[dinosaure]

The problem is the same as ocaml-freestanding when ocaml-ci wants to run dune and ... this project is just a spaguetti of Makefile...

[dinosaure]

The CI works but it does not compile gilbraltar (only gilbraltar-toolchain). The main problem is: we need the OPAM layout to, finally, build our test and OCaml-CI does not provide to us such ability.