Task: deps(opam): Check and improve the CI if need be (to spot missing deps)

[erikmd]

Related user(s):

@erikmd

Related issue(s) or PR(s):

• Bug: docker build failure, bogus pinned package versions, "Toplevel not initialized" #621
• build: update pinned package versions #622

Related project scope(s):

other

The problem:

Given the new archival strategy in opam-repository (cf. https://discuss.ocaml.org/t/opam-repository-archival-phase-3/16748), issues such as #621 can occur anew at some point.

Wanted solution:

• Double-check that learn-ocaml's GHA jobs will be able to spot such issues
• Ensure that these checks are involved in the weekly scheduled workflow

Considered alternatives:

No response

Additional context:

No response