Upper bound qcheck-core in containers 3.9-3.16

[jmid]

The forthcoming QCheck 0.26 release in #28148 patches the float generators to avoid blind spots: c-cube/qcheck#350.
The CI run for the release however revealed such a blind spot, causing a containers QCheck test to start failing when run with QCheck 0.26:
https://opam.ci.ocaml.org/github/ocaml/opam-repository/commit/c715a95fe87d4397d1f0658b2ae5acd528de705e

This PR therefore adds an upper bound of qcheck-core for containers for already existing releases, so that their tests run predictably.

I've filed an upstream PR to restore the property for the next containers release: c-cube/ocaml-containers#478

[jmid]

I saw the CI failing on OCaml 5.4.0~alpha1 and indeed only the recent 3.16 release supports 5.4.0:
https://github.com/c-cube/ocaml-containers/releases/tag/v3.16 and c-cube/ocaml-containers#477
I've therefore added corresponding ocaml upper bounds for containers 3.7-3.15 while here... 🙂

[jmid]

CI summary:

• 2 sihl-core jobs failed
• several embedded_ocaml_templates.0.8 due to expect test failures: Error: This expression has type string vs Error: This expression has type "string"
• 2 times (on Fedora and ARM64) a test fails with Failure("uniformity check failed")
• 3 failures to build on FreeBSD

None of these are caused by setting qcheck-core and ocaml bounds (to known releases).
As such, this should be good to go.

[mseri]

Thanks