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

tests/test-lock.py

@@ -141,7 +141,7 b' class testlock(unittest.TestCase):'
         state.assertacquirecalled(True)
 
         # fake a fork
-        forklock = copy.deepcopy(lock)
+        forklock = copy.copy(lock)
         forklock._pidoffset = 1
         forklock.release()
         state.assertreleasecalled(False)
@@ -238,7 +238,7 b' class testlock(unittest.TestCase):'
             childstate.assertacquirecalled(True)
 
             # fork the child lock
-            forkchildlock = copy.deepcopy(childlock)
+            forkchildlock = copy.copy(childlock)
             forkchildlock._pidoffset += 1
             forkchildlock.release()
             childstate.assertreleasecalled(False)