fix: Use C.UTF-8 locale

available since glibc 2.35 as en_US.UTF-8 is not available in moste of the 195 countries of the world.

https://sourceware.org/glibc/wiki/Proposals/C.UTF-8

$ make check
...
INTERNAL_OSINFO_DB_DATA_DIR=data INTERNAL_OSINFO_DB_DATA_SRC_DIR=data python3 -m pytest tests
INTERNALERROR> Traceback (most recent call last):
INTERNALERROR>   File "/usr/lib/python3/dist-packages/_pytest/main.py", line 236, in wrap_session
INTERNALERROR>     config._do_configure()
INTERNALERROR>   File "/usr/lib/python3/dist-packages/_pytest/config/__init__.py", line 911, in _do_configure
INTERNALERROR>     self.hook.pytest_configure.call_historic(kwargs=dict(config=self))
INTERNALERROR>   File "/usr/lib/python3/dist-packages/pluggy/hooks.py", line 308, in call_historic
INTERNALERROR>     res = self._hookexec(self, self.get_hookimpls(), kwargs)
INTERNALERROR>   File "/usr/lib/python3/dist-packages/pluggy/manager.py", line 92, in _hookexec
INTERNALERROR>     return self._inner_hookexec(hook, methods, kwargs)
INTERNALERROR>   File "/usr/lib/python3/dist-packages/pluggy/manager.py", line 83, in <lambda>
INTERNALERROR>     self._inner_hookexec = lambda hook, methods, kwargs: hook.multicall(
INTERNALERROR>   File "/usr/lib/python3/dist-packages/pluggy/callers.py", line 208, in _multicall
INTERNALERROR>     return outcome.get_result()
INTERNALERROR>   File "/usr/lib/python3/dist-packages/pluggy/callers.py", line 80, in get_result
INTERNALERROR>     raise ex[1].with_traceback(ex[2])
INTERNALERROR>   File "/usr/lib/python3/dist-packages/pluggy/callers.py", line 187, in _multicall
INTERNALERROR>     res = hook_impl.function(*args)
INTERNALERROR>   File "tests/conftest.py", line 27, in pytest_configure
INTERNALERROR>     locale.setlocale(locale.LC_CTYPE, 'en_US.UTF-8')
INTERNALERROR>   File "/usr/lib/python3.9/locale.py", line 610, in setlocale
INTERNALERROR>     return _setlocale(category, locale)
INTERNALERROR> locale.Error: unsupported locale setting
make: *** [Makefile:99: check] Fehler 3