add py{27,3}-from-forge to clients project to ensure we don't break everything when releasing

Right now we've have broken francearchives by releasing too fast, it would be great to add "from-forge" tests in the client projects .gitlab-ci.yaml like on our core projects, for example:

https://forge.extranet.logilab.fr/open-source/CubicWeb/RQL/blob/dfb56a59993f12383e5b66e77059dca1b6ed26ca/tox.ini#L9-18

https://forge.extranet.logilab.fr/open-source/CubicWeb/RQL/blob/dfb56a59993f12383e5b66e77059dca1b6ed26ca/.gitlab-ci.yml#L14-16

I'm putting this on 3.28 because it would be great to have it but I don't think it's blocking.

Also I don't have access to enough client projects to do this by myself but I'm know it's a WIP on francearchives for example.