Work around an issue where getaddrinfo() returns duplicate entries

This commit works around an issue where getaddrinfo() can return
duplicate entries on some systems, causing bind() to fail when it
attempts to listen on the same address/port more than once. Thanks
go to Colin Watson for reporting this issue and suggesting a fix.

Author: ronf

asyncssh/listener.py

@@ -25,7 +25,7 @@
 import socket
 from types import TracebackType
 from typing import TYPE_CHECKING, AnyStr, Callable, Generic, List, Optional
-from typing import Sequence, Tuple, Type, Union
+from typing import Sequence, Set, Tuple, Type, Union
 from typing_extensions import Self
 
 from .forward import SSHForwarderCoro
@@ -285,9 +285,19 @@ async def create_tcp_local_listener(
     if not addrinfo: # pragma: no cover
         raise OSError('getaddrinfo() returned empty list')
 
+    seen_addrinfo: Set[Tuple] = set()
     servers: List[asyncio.AbstractServer] = []
 
-    for family, socktype, proto, _, sa in addrinfo:
+    for addrinfo_entry in addrinfo:
+        # Work around an issue where getaddrinfo() on some systems may
+        # return duplicate results, causing bind to fail.
+        if addrinfo_entry in seen_addrinfo: # pragma: no cover
+            continue
+
+        seen_addrinfo.add(addrinfo_entry)
+
+        family, socktype, proto, _, sa = addrinfo_entry
+
         try:
             sock = socket.socket(family, socktype, proto)
         except OSError: # pragma: no cover