Fix grouping year reference in add_land_use_constraint_m

[tgi-climact]

Fix grouping year reference from grouping_years to grouping_years_power in add_land_use_constraint_m.

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.

[tgi-climact]

@fneum Could be usefull to add to tests a scenario with m option for clusters (https://github.com/PyPSA/pypsa-eur/blob/master/config/test/config.myopic.yaml#L19). What do you think about it ?

[FabianHofmann]

@fneum Could be usefull to add to tests a scenario with m option for clusters (https://github.com/PyPSA/pypsa-eur/blob/master/config/test/config.myopic.yaml#L19). What do you think about it ?

that is probably a good idea, however we have to keep in mind to not bloat the CI resources/time
EDIT: If you want to propose something, that's most welcome