Frama-C 26-beta: multiple fixes
Frama-C 26-beta: multiple fixes

- remove version from depopts
- conflicts with cairo2 < 0.6.2, mlmpfr < 4.1.0-bugfix2, pilat <= 1.6, result < 1.5
- disabled tests for macos (no realpath command)
- force GTK2 for macos, GTK3 for Linux

nberth/opam-repository,ocaml/opam-repository,nberth/opam-repository,ocaml/opam-repository,pirbo/opam-repository,pirbo/opam-repository