Closes #1599.

Changes proposed in this Pull Request

Drop link indices not in n.buses to prevent the script from failing with a KeyError. In principle, this applies the same logic as plot_power_network.py:126

# drop non-bus
to_drop = costs.index.levels[0].symmetric_difference(n.buses.index)
if len(to_drop) != 0:
    logger.info(f"Dropping non-buses {to_drop.tolist()}")
    costs.drop(to_drop, level=0, inplace=True, axis=0, errors="ignore")

where non-buses are being dropped already.

Checklist

• I tested my contribution locally and it works as intended.
• Code and workflow changes are sufficiently documented.
• Changed dependencies are added to envs/environment.yaml.
• Changes in configuration options are added in config/config.default.yaml.
• Changes in configuration options are documented in doc/configtables/*.csv.
• Sources of newly added data are documented in doc/data_sources.rst.
• A release note doc/release_notes.rst is added.