fix(attribute or function): Allows to apply function or get attributes on projection variable with eid relation

This allows to query something like "Any X.attribute WHERE X eid 42"
The query was simplified using the syntax "Any 42" and the attribute could not be reached.

type:ignore comments are used to silence mypy errors
let's remove the ones that are not anymore necessary

related: cubicweb#528

These types are not supposed to be accessed by client code.

TypeVars should be referenced at least twice otherwise they have no effect.

Add a job that will:
- clone the last Cubicweb version
- update rql requirement within Cubicweb's setup.py
- finally, run tox -e py3-server

See #8

Searched across all projects on the forge.