Update array_hash_map.py (#1803)

基于数组实现的哈希表中，`get()` 函数的返回值还可能会 None；且 `put()` 函数不仅可添加键值对、还可更新表中已有键值对的值；

codes/python/chapter_hashing/array_hash_map.py

@@ -26,7 +26,7 @@ class ArrayHashMap:
         index = key % 100
         return index
 
-    def get(self, key: int) -> str:
+    def get(self, key: int) -> str | None:
         """查询操作"""
         index: int = self.hash_func(key)
         pair: Pair = self.buckets[index]
@@ -35,7 +35,7 @@ class ArrayHashMap:
         return pair.val
 
     def put(self, key: int, val: str):
-        """添加操作"""
+        """添加和更新操作"""
         pair = Pair(key, val)
         index: int = self.hash_func(key)
         self.buckets[index] = pair