Remove < 4.08 from supported releases

[benmandrew]

According to this thread https://discuss.ocaml.org/t/raising-the-minimum-tested-version-of-ocaml-to-4-05-or-4-08-from-4-02/12464 the lower bound of tested OCaml versions should be raised to 4.08. This will save significant compute time for CI.

Required for ocurrent/opam-repo-ci#259.

@tmattio @avsm

[avsm]

Before we do this, the opam-repository needs to have a model for how we handle the lower bound for new packages. Should all incoming packages be marked as >={4.08} from now on unless manually tested with something earlier? I think that's probably the safest thing to do...

[punchagan]

Before we do this, the opam-repository needs to have a model for how we handle the lower bound for new packages. Should all incoming packages be marked as >={4.08} from now on unless manually tested with something earlier? I think that's probably the safest thing to do...

So, if I'm reading this right, we want to enforce ocaml>={4.08} for all new incoming updates to the opam-repository, right? Would adding a lint to this effect to opam-repo-ci that ensures this lower bound be sufficient? Or did you have anything else in mind?

[punchagan]

Note to self (and anyone new to the issue): The deprecation strategy is being discussed here