Adjust currency_year with inflation adjustment

[euronion]

Before: currency_year in the outputs/ was always reflecting the input data currency year.
After this PR: Inflation adjustment changes the currency_year to reflect the year of the inflation adjustment.

Changes proposed in this Pull Request

Checklist

• Code changes are sufficiently documented; i.e. new functions contain docstrings and further explanations may be given in doc.
• Data source for new technologies is clearly stated.
• Newly introduced dependencies are added to environment.yaml (if applicable).
• A note for the release notes doc/release_notes.rst of the upcoming release is included.
• I consent to the release of this PR's code under the GPLv3 license.