python 3.13.0a6 tests throw errors due to pickling a _ThreadHandle

[mmckerns]

Tests seem to error out due to: uqfoundation/dill#654

Basically...

$ python test_multiprocessing_forkserver/test_manager.py 
EEEEEEE.sEEEEE.EEE........E....E........s.s.s.....s...s...ss.EE.E.ssE.E..s

where all errors end in:

  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/pickle.py", line 574, in save
    rv = reduce(self.proto)
         ~~~~~~^^^^^^^^^^^^
TypeError: cannot pickle '_thread._ThreadHandle' object

Interestingly, 3.13.0a5 doesn't trigger any errors, while the code is nearly identical.

[mmckerns]

should be closed due to dill #679