Closes # (if applicable).

Changes proposed in this Pull Request

fix mock_snakemake for use in pypsa-ariadne (and similiar projects)

Checklist

• [x ] I tested my contribution locally and it seems to work fine.
• [x ] Code and workflow changes are sufficiently documented.
• [x ] Changed dependencies are added to envs/environment.yaml.
• Changes in configuration options are added in all of config.default.yaml.
• Changes in configuration options are also documented in doc/configtables/*.csv.
• A release note doc/release_notes.rst is added.