Prevent qfs.0.12 from building on OCaml 5
FTBFS due to depending on `Stream`:
#=== ERROR while compiling qfs.0.12 ===========================================#
# context 2.2.0~alpha~dev | linux/x86_64 | ocaml-base-compiler.5.0.0 | file:///home/opam/opam-repository
# path ~/.opam/5.0/.opam-switch/build/qfs.0.12
# command ~/.opam/opam-init/hooks/sandbox.sh build ocaml setup.ml -configure --prefix /home/opam/.opam/5.0
# exit-code 2
# env-file ~/.opam/log/qfs-8-f5153f.env
# output-file ~/.opam/log/qfs-8-f5153f.out
### output ###
# File "./setup.ml", line 575, characters 4-15:
# 575 | Stream.from next
# ^^^^^^^^^^^
# Error: Unbound module Stream