Hotfix for n.statistics.installed_capacity

[lindnemi]

Partially addresses #1093.

Fixes p_nom to p_nom_min for renewable generators with grouping_year == baseyear. Since these are extendable p_nom will be ignored by the optimization. On the other hand, n.statistics.installed_capacity will report the correct values.

Checklist

• I tested my contribution locally and it seems to work fine.
• Code and workflow changes are sufficiently documented.
• 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.