fix sector coupeled model for single, non EU28 countries - e.g. UA

[martacki]

Closes # (if applicable).

Changes proposed in this Pull Request

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.

[yerbol-akhmetov]

@martacki, tested, works fine with PR on config https://github.com/instrat-pl/ukraine-energy-modelling/pull/9

[martacki]

@yerbol-akhmetov by any chance, did you also test for default config? It worked on my end, but would be nice to check on 2 machines just to be sure :)

[yerbol-akhmetov]

@yerbol-akhmetov by any chance, did you also test for default config? It worked on my end, but would be nice to check on 2 machines just to be sure :)

@martacki, have checked with open model config. I haven't tried for default one because it does not focus on Ukraine by default. But let me check it and get back.