Annotates indexers/utils.py functions that don't return anything wi…

…th `None` (pandas-dev#43893)

pandas/core/indexers/utils.py

@@ -363,7 +363,7 @@ def length_of_indexer(indexer, target=None) -> int:
     raise AssertionError("cannot find the length of the indexer")
 
 
-def deprecate_ndim_indexing(result, stacklevel: int = 3):
+def deprecate_ndim_indexing(result, stacklevel: int = 3) -> None:
     """
     Helper function to raise the deprecation warning for multi-dimensional
     indexing on 1D Series/Index.
@@ -409,7 +409,7 @@ def unpack_1tuple(tup):
     return tup
 
 
-def check_key_length(columns: Index, key, value: DataFrame):
+def check_key_length(columns: Index, key, value: DataFrame) -> None:
     """
     Checks if a key used as indexer has the same length as the columns it is
     associated with.