Adapt to mirage 3.11

[samoht]

Testing my conduit changes.

[samoht]

The xen backend is failing with:

mirage-unikernel-www-xen is now pinned to file:///home/opam/www/src (version ~dev)
# Detecting depexts using vars: arch=x86_64, os=linux, os-distribution=alpine, os-family=alpine
[ERROR] No solution for mirage-unikernel-www-xen: The following dependencies couldn't be met:
          - mirage-unikernel-www-xen -> mirage-xen >= 5.0.0 -> mirage-xen-ocaml >= 3.3.1 -> ocaml < 4.09.0
              base of this switch (use `--unlock-base' to force)


Command failed: opam list --readonly --external  --resolve=mirage-unikernel-www-xen returned 20

[samoht]

All green now that I've removed the dependency to base in mirage/ocaml-cohttp#745 🎉

[dinosaure]

All is fixed on #702/released now, thanks for your patch 👍.