This is because America/Godthab was renamed to America/Nuuk in tz 2020a and the former is now only in tzdata-legacy.
Adding tzdata-legacy to build depends fixes the build but a better fix is probably to update libgweather4's data to follow the tz database changes. I filed https://gitlab.gnome.org/GNOME/libgweather/-/merge_requests/311 upstream about this.
