tests: perform a shallow copy instead of a deep copy
Python 3 can't perform a deep copy because it looks like symbols
in the locals() namespace are not deep-copyable. For the curious,
somehow the deepcopy() is attempting to copy objects attached to
the unittest.* functions for the running test!
We don't use deepcopy() anywhere in the code base and a shallow
object copy should be sufficient to test lock copying.
Actually, I'm not sure why we even test this, as I couldn't find
copy.copy() being used for lock copying either. Who knows.
Differential Revision: https://phab.mercurial-scm.org/D5770