[ci] put ocamlbuild in the opam root since some packages need it
[ci] put ocamlbuild in the opam root since some packages need it

coq/opam-coq-archive,gmalecha/opam-coq-archive,gmalecha/opam-coq-archive,gmalecha/opam-coq-archive,mattam82/coq-opam-archive,mattam82/coq-opam-archive,mattam82/coq-opam-archive