ocaml-qcheck: autopkgtest failures with ocaml-dune 3.9

Imported from Debian bug http://bugs.debian.org/1040893:

Source: ocaml-qcheck
Version: 0.20-1
Severity: normal
X-Debbugs-Cc: <email address hidden>

Dear Maintainer,

On Sid and Ubuntu Mantic, autopkgtest failures can be observed.

The first failure has to do with dropping the dune -> ocaml-dune transitional
package:
  Package dune is not available, but is referred to by another package.
  This may mean that the package is missing, has been obsoleted, or
  is only available from another source
  However the following packages replace it:
    ocaml-dune

  E: Package 'dune' has no installation candidate
Updating the package name in the test dependencies is sufficient.

If that is resolved, the following failure is seen:
  autopkgtest [20:11:29]: test test: [-----------------------
  Error: No dune-project file has been found. A default one is assumed but the
  project might break when dune is upgraded. Please create a dune-project file.
  Hint: generate the project file with: $ dune init project <name>
  autopkgtest [20:11:30]: test test: -----------------------]

To address the second problem, I propose adding a dune-project file for
autopkgtest use.

Please see the attached debdiff which addresses both of the above issues.
Thanks.

-Dan

(patch omitted on launchpad as I'm not seeking sponsorship)