[lit] Bump up the Windows process cap from 32 to 60

At 61 or over, I see messages like

  File "...\Python\Python39\lib\multiprocessing\connection.py", line 816, in _exhaustive_wait
    res = _winapi.WaitForMultipleObjects(L, False, timeout)

  ValueError: need at most 63 handles, got a sequence of length 64

60 seems to work for me.

If this causes issues for anybody else, feel free to revert.