create_unix_server() removes listening unix socket, potentially from other process

Bug report

Bug description:

I made a mistake leading to reusing the same unix socket path for multiple Python processes, then as a surprise realized only the last process's unix socket listening, and none will be listening if the last process stopped.

I then realized this was implemented in https://github.com/python/asyncio/pull/441 for https://bugs.python.org/issue28399 which isn't clear on why deleting the original unix socket make sense. Assumingly it is for removing old unix socket files that's not in use, but apparently it can be removing listening sockets as well.

I don't think this should be intended behavior but open to any comment. Thanks.

To reproduce, with repro.py as below:

import os
import asyncio


class IdentityProtocol(asyncio.Protocol):
    """a protocol that politely replies server's pid then close connection"""

    def connection_made(self, transport):
        print('got new connection')
        transport.write(b'hello from pid=%d\r\n' % os.getpid())
        transport.close()


async def main():
    server = await asyncio.get_running_loop().create_unix_server(
            lambda: IdentityProtocol(), 'duplicatedpath.sock'
        )
    async with server:
        await server.serve_forever()


asyncio.run(main())

run two of such instances in separate terminals for the same working directory, and after each process created, use nc -CU duplicatedpath.sock which should simply show the pid of the last python process and exit.

CPython versions tested on:

3.10

Operating systems tested on:

Linux

先在 Linux 上使用提供的 repro.py 和 nc 命令重現該行為，接著追蹤 asyncio.create_unix_server() 並檢視連結的 PR 441 和 issue 28399。當 socket 清理行為不再刪除其他程序正在監聽的 Unix socket，且回報的情境由回歸測試涵蓋時，即表示完成。