Cram test support seems too limited for Coq

[rlepigre]

Desired Behavior

Cram tests where Coq code is built (with dune) against a coq theory from a local package (explicit dependency being given) fails by not finding the library. Ideally, this would just work as the analogous code in OCaml (see https://github.com/ocaml/dune/pull/6011).

Example

An example (in the form of a reproducing test case) is given in https://github.com/ocaml/dune/pull/6014.