[Feature] Remove manual .condarc creation in continuous integration

[jan-janssen]

@liamhuber suggested to use:

        python-version: '3.13'
        miniforge-version: latest
        channels: conda-forge
        conda-remove-defaults: true
        environment-file: .ci_support/environment-mpich.yml

The addition of conda-remove-defaults: true should resolve the need to create a manual config.

[jan-janssen]

I did the most recent testing in pyiron/atomistics#433