toplevel_expect_test.v0.15.0: use ocaml < 5
See #23989
#=== ERROR while compiling toplevel_expect_test.v0.15.0 =======================#
# 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/toplevel_expect_test.v0.15.0
# command ~/.opam/opam-init/hooks/sandbox.sh build dune build -p toplevel_expect_test -j 47
# exit-code 1
# env-file ~/.opam/log/toplevel_expect_test-7-8679e0.env
# output-file ~/.opam/log/toplevel_expect_test-7-8679e0.out
### output ###
[...]
# File "src/main.ml", line 526, characters 2-23:
# 526 | Clflags.unsafe_string := Toplevel_backend.unsafe_string ();
# ^^^^^^^^^^^^^^^^^^^^^
# Error: Unbound value Clflags.unsafe_string