AttributeError on `_lock` with Unix socket connection

[soonum]

Describe the bug

I use aioredis to connect to a Redis instance via Unix socket. Since I've bumped to the version 2.0.1 of the lib I encounter an error.
This seems related to this commit. After digging a bit in the code, I've noticed that on UnixDomainSocketConnection instantiation doesn't perform a super().__init__ nor refrence a self._lock. Adding a self._lock = asyncio.Lock() solves my issue.

If this is this the only thing to fix I could do a PR.

To Reproduce

import asyncio
import aioredis

client = aioredis.from_url("unix://@/a/path/to/redis.sock")
loop = asyncio.get_event_loop()
loop.run_until_complete(client.ping())

Expected behavior

A simple command such as ping should pass.

Logs/tracebacks

Traceback (most recent call last):
  File "/home/code/retrieve_cancel.py", line 60, in <module>
    loop.run_until_complete(client.ping())
  File "/home/code/python/lib/python3.9/asyncio/base_events.py", line 642, in run_until_complete
    return future.result()
  File "/home/code/python/lib/python3.9/site-packages/aioredis/client.py", line 1085, in execute_command
    return await self.parse_response(conn, command_name, **options)
  File "/home/code/python/lib/python3.9/site-packages/aioredis/client.py", line 1101, in parse_response
    response = await connection.read_response()
  File "/home/code/python/lib/python3.9/site-packages/aioredis/connection.py", line 898, in read_response
    async with self._lock:
AttributeError: _lock

Python Version

Python 3.9.7

aioredis Version

Version: 2.0.1

Additional context

No response

Code of Conduct

• I agree to follow the aio-libs Code of Conduct

[Andrew-Chen-Wang]

Please create the necessary PR for this. I'm not sure if we test on Unix socket connection; if we don't, then a simple addition without a test case will do. Thank you!