use native union type syntax

unwind/types.py

@@ -1,5 +1,5 @@
 import re
-from typing import Union, cast
+from typing import cast
 
 import ulid
 from ulid.hints import Buffer
@@ -16,7 +16,7 @@ class ULID(ulid.ULID):
 
     _pattern = re.compile(r"^[0-9A-HJKMNP-TV-Z]{26}$")
 
-    def __init__(self, buffer: Union[Buffer, ulid.ULID, str, None] = None):
+    def __init__(self, buffer: Buffer | ulid.ULID | str | None = None):
         if isinstance(buffer, str):
             if not self._pattern.search(buffer):
                 raise ValueError("Invalid ULID.")