The test case came from test_generators, not test_itertools.
Ensure there's no cyclic garbage we are counting.

This is weird because it leaks, then reaches a limit:

python.exe -i test_tee.py
>>> leak()
0
[26633 refs]
>>> leak()
0
[26658 refs]
>>> leak()
0
[26683 refs]
>>> leak()
0
[26708 refs]
>>> leak()
0
[26708 refs]
>>> leak()
0
[26708 refs]
>>> leak()
0