Use older style of type hint for Python 3.6 compat

mailman_sync.py

@@ -1,5 +1,7 @@
 #!/usr/bin/env python3
 
+from typing import List
+
 """
 Update Mailman 2 lists via a json API of the form {"LIST": ["ADDRESS", ...]}
 """
@@ -11,7 +13,7 @@ import subprocess
 import requests
 
 
-def sync_members(mailman_bin: Path, mailing_list: str, members: list[str]):
+def sync_members(mailman_bin: Path, mailing_list: str, members: List[str]):
     members_file = "\n".join(members)
     output = subprocess.run(
         [