Publish wheels to test.pypi.org

[crusaderky]

versioned-hdf5 CI has the option to publish to test.pypi.org:

versioned-hdf5/.github/workflows/pypi_publish.yml

Lines 90 to 95 in e5f4053

	- name: 🧪 Publish to PyPI Testing
	uses: pypa/gh-action-pypi-publish@release/v1
	if: ${{ inputs.test_pypi }}
	with:
	repository-url: https://test.pypi.org/legacy/
	packages-dir: wheels

To trigger it, one needs to go to https://github.com/deshaw/versioned-hdf5/actions/workflows/pypi_publish.yml and manually start a run:

However, the workflow currently fails because there is no https://test.pypi.org/project/versioned-hdf5/
e.g.
https://github.com/deshaw/versioned-hdf5/actions/runs/16264867141/job/45918586633

It would be useful to have this functionality. The new project should be created as an exact copy of https://pypi.org/project/versioned-hdf5/.
Once the manual workflow works, it would be trivial e.g. to use this for dev builds that are triggered on every merge to master.

This would also be very useful to have a easy URL to test changes to the conda-forge recipe before a new release is ready.

See also: https://github.com/pypa/gh-action-pypi-publish?tab=readme-ov-file#advanced-release-management

CC @peytondmurray @ArvidJB