[Typing][C-65] Add type annotations for python/paddle/incubate/multiprocessing/reductions.py (#66030)

Author: megemini

python/paddle/incubate/multiprocessing/reductions.py

@@ -232,7 +232,7 @@ def _reduce_lodtensor(lodtensor):
     return (rebuild, (type(lodtensor),) + metadata)
 
 
-def init_reductions():
+def init_reductions() -> None:
     if not _supported_check():
         return