Version : the proposal is not working when no tags have been set up

[pradal]

There is a need of intermediate version without releasing the package.
And the version inherited from the tag system seems to not be sufficient.

For me the versionning is not clear enough.
I do not understand how it works and on my test, it does not always work.

See https://github.com/openalea/core/actions/runs/15073228664 where no version was set on the master.

[pradal]

Add a solution when tags are not available:

build:
  # [...]
  script_env:
    - SETUPTOOLS_SCM_PRETEND_VERSION={{version}}
  script: "{{ PYTHON }} -m pip install . -vv"