E741: regression for `re.I` as a default parameter

[asottile]

def f(x=re.I):
    pass

2.5.0:

$ python -m pycodestyle t.py
$

2.6.0:

$ python -m pycodestyle t.py
t.py:1:12: E741 ambiguous variable name 'I'

originally reported here

regression appears to be introduced by b8db33dfa6cd4029b75efd1e7cab7c1b64d03bc7 via git bisect CC @rettenbs