session 0.4.1: test not compatible with ocaml 5

Does not link unix:
```
=== ERROR while compiling session.0.4.1 ======================================#
 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/session.0.4.1
 command              ~/.opam/opam-init/hooks/sandbox.sh build dune runtest -p session -j 255
 exit-code            1
 env-file             ~/.opam/log/session-8-5abb27.env
 output-file          ~/.opam/log/session-8-5abb27.out
 (cd _build/default && /home/opam/.opam/5.0/bin/ocamlopt.opt -w -40 -g -o lib_test/memory/test.exe /home/opam/.opam/5.0/lib/bigarray-compat/bigarray_compat.cmxa /home/opam/.opam/5.0/lib/cstruct/cstruct.cmxa -I /home/opam/.opam/5.0/lib/cstruct /home/opam/.opam/5.0/lib/zarith/zarith.cmxa -I /home/opam/.opam/5.0/lib/zarith /home/opam/.opam/5.0/lib/sexplib0/sexplib0.cmxa /home/opam/.opam/5.0/lib/base/caml/caml.cmxa /home/opam/.opam/5.0/lib/parsexp/parsexp.cmxa /home/opam/.opam/5.0/lib/sexplib/sexplib.cmxa /home/opam/.opam/5.0/lib/ppx_sexp_conv/runtime-lib/ppx_sexp_conv_lib.cmxa /home/opam/.opam/5.0/lib/result/result.cmxa /home/opam/.opam/5.0/lib/ppx_deriving/runtime/ppx_deriving_runtime.cmxa /home/opam/.opam/5.0/lib/nocrypto/nocrypto.cmxa -I /home/opam/.opam/5.0/lib/nocrypto lib/session.cmxa /home/opam/.opam/5.0/lib/ocaml/unix/unix.cmxa /home/opam/.opam/5.0/lib/stdlib-shims/stdlib_shims.cmxa /home/opam/.opam/5.0/lib/ounit2/advanced/oUnitAdvanced.cmxa /home/opam/.opam/5.0/lib/ounit2/oUnit.cmxa /home/opam/.opam/5.0/lib/nocrypto/nocrypto_unix.cmxa -I /home/opam/.opam/5.0/lib/nocrypto lib_test/session_test.cmxa lib_test/memory/.test.eobjs/native/test.cmx)
 File "_none_", line 1:
 Error: No implementations provided for the following modules:
          Unix referenced from lib/session.cmxa(Session__Memory)
```

Signed-off-by: Marcello Seri <[email protected]>

Author: mseri

packages/session/session.0.4.1/opam

@@ -15,7 +15,7 @@ depends: [
 build: [
   ["dune" "subst"] {dev}
   ["dune" "build" "-p" name "-j" jobs]
-  ["dune" "runtest" "-p" name "-j" jobs] {with-test}
+  ["dune" "runtest" "-p" name "-j" jobs] {with-test & ocaml:version < "5.0.0"}
 ]
 dev-repo: "git+https://github.com/inhabitedtype/ocaml-session.git"
 synopsis: "A session manager for your everyday needs"