When regrtest in run inside IDLE, sys.stdout and sys.stderr are not
TextIOWrapper objects and have no file descriptor associated:
sys.stderr.fileno() raises io.UnsupportedOperation.
Disable faulthandler and don't replace sys.stdout in that case.
Issue #26538: libregrtest: Fix setup_tests() to keep module.__path__ type
(_NamespacePath), don't convert to a list.
Add _NamespacePath.__setitem__() method to importlib._bootstrap_external.