Copy sys.module.items() in case it changes during iteration. (#34592)

Co-authored-by: Claude <cvandermerwe@google.com>

Author: claudevdm

sdks/python/apache_beam/internal/cloudpickle_pickler.py

@@ -82,7 +82,7 @@ def _get_proto_enum_descriptor_class():
 
 
 def _reconstruct_enum_descriptor(full_name):
-  for _, module in sys.modules.items():
+  for _, module in list(sys.modules.items()):
     if not hasattr(module, 'DESCRIPTOR'):
       continue