AF_DECnet is missing from socket.AddressFamily

Bug report

Bug description:

This code populates the AddressFamily enum:

IntEnum._convert_(
        'AddressFamily',
        __name__,
        lambda C: C.isupper() and C.startswith('AF_'))

But AF_DECnet isn't all uppercase so it's currently excluded. Do we need the isupper() test? I don't see anything that begins with AF_ in socket other than the existing members of AddressFamily and AF_DECnet.

CPython versions tested on:

3.13

Operating systems tested on:

macOS

Linked PRs

• gh-127548

从 socket 模块开始，该模块中的 AddressFamily 由 IntEnum.convert() 填充，并检查 AF_* 名称，尤其是 AF_DECnet。查看链接的 PR gh-127548 和现有的 socket 测试；完成的标准是 AF_DECnet 在 socket.AddressFamily 中得到表示，且不会导致其他地址族成员出现回归。