pkg: relax version constraints for ocamlformat dev tool

[gridbugs]

trafficstars

Previously dune would install the exact version of ocamlformat specified in the .ocamlformat file in the project's root. This prevents alternative distributions of the ocamlformat package from being used, as these typically append a suffix to the version number.

The motivation for this change is supporting a binary dev tools distribution where the ocamlformat package is named like "ocamlformat.0.26.2+binary", and we want that package to be installable when the .ocamlformat file of a project specifies "version=0.26.2".

[moyodiallo]

Would you like to add a test ?

[gridbugs]

Added a test