bugfixing for optimist and pessimist cost data and fixing environment yaml

[toniseibold]

Optimist and Pessimist cost data did not work due to two minor bugs. Maybe think about adding them to the CI check since running technology-data does not take too much time. The environment.yaml was not working for the mock_snakemake. Missing packages like pypsa and snakemake version > 8.0 necessary.

Closes # (if applicable).

Changes proposed in this Pull Request

• bugfixing
• updating environment.yaml

Checklist

• [ ] Code changes are sufficiently documented; i.e. new functions contain docstrings and further explanations may be given in doc.
• [ ] Data source for new technologies is cleary stated.
• [x] Newly introduced dependencies are added to environment.yaml (if applicable).
• [ ] A note for the release notes doc/release_notes.rst of the upcoming release is included.
• [x] I consent to the release of this PR's code under the GPLv3 license.