Missing investment cost data for `geothermal` technology

[danielelerede-oet]

Checklist

• I am using the current master branch or the latest release. Please indicate:

Describe the Bug

The output cost files are not reporting investment cost data for the geothermal technology despite being present in input files (e.g. costs_pypsa.py). I noticed that for geothermal but may be a more widespread issue.

[lisazeyen]

maybe @LukasFrankenQ remembers for geothermal, did we agree that it is better to remove the add_egs_data function from here and calculate all within PyPSA-Eur or is this a bug?