region error: Greece

[Renato-Rodrigues]

While working on this pull request, #154, I got an unrelated error in the automated tests:

=================================== FAILURES ===================================
_______________________________ test_iso_mapping _______________________________

    def test_iso_mapping():
        # check that iso-mapping dictionary is not empty and has specific elements
        for name in ["GR", "GRC", "EL"]:
>           assert iso_mapping[name] == "Greece"
E           KeyError: 'GR'

tests/test_core.py:7: KeyError
_____________________________ test_nuts_hierarchy ______________________________

    def test_nuts_hierarchy():
        # check that nuts-hierarchy is not empty and has specific elements
>       assert nuts_hierarchy["Belgium"]["BE2"]["BE24"] == ["BE241", "BE242"]
E       KeyError: 'Belgium'

tests/test_core.py:12: KeyError
=========================== short test summary info ============================
FAILED tests/test_core.py::test_iso_mapping - KeyError: 'GR'
FAILED tests/test_core.py::test_nuts_hierarchy - KeyError: 'Belgium'
======================== 2 failed, 18 passed in 55.[69](https://github.com/openENTRANCE/openentrance/runs/5183941245?check_suite_focus=true#step:5:69)s =========================
Error: Process completed with exit code 1.

[danielhuppmann]

Thanks @Renato-Rodrigues, I also just saw this in #153 by @JohannesEmm... Will take a look in a minute.