Fix import errors in pylint CI job

In the pylint CI job many of these errors occur and cause low pylint score.

tests/test_functions.py:8:0: E0401: Unable to import 'virtmat.language.utilities.types' (import-error)
tests/test_functions.py:8:0: E0611: No name 'language' in module 'virtmat' (no-name-in-module)