fix unknown encoding: utf-8-sig

Fix for:
Fatal Python error: init_import_site: Failed to import the site module
Python runtime state: initialized
Traceback (most recent call last):
  File "<frozen importlib._bootstrap>", line 1371, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1342, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 938, in _load_unlocked
  File "<frozen importlib._bootstrap>", line 1179, in exec_module
  File "<frozen site>", line 723, in <module>
  File "<frozen site>", line 709, in main
  File "<frozen site>", line 382, in addusersitepackages
  File "<frozen site>", line 254, in addsitedir
  File "<frozen site>", line 197, in addpackage
LookupError: unknown encoding: utf-8-sig