Add test of conda install

The problem

As a user, if I release the package on conda, I want to check the install from conda too. Currently, this doesn't happen.

Definition of "done"

• add test of installation from conda to the template's GitHub CI
• add test of installation from conda to the template's GitLab CI

Additional context

There is a working example to build from here: https://github.com/climate-resource/input4mips_validation/blob/main/.github/workflows/install-conda.yaml. That would need to be combined with the latest learning in our PyPI install workflow to create a nice product.