transaction task not correctly exited at asyncio.exceptions.CancelledError

Describe the bug
I was using get_or_create as part of my atomic operation, basically tested it with exiting the task real quick. Then I found some errors blocking the server before it shutdown.

To Reproduce
[Code]
here is part of the code in a sanic server, routing to a websocket blueprint

bp_ws = Blueprint("Websockets", url_prefix="/ws")

@bp_ws.websocket("/file/<pk>/")
async def feed(request, ws, pk):
    await Room.get_or_create(channel_name='test_channel')

[Do]

1. Run server
2. use postman to connect to the websocket
3. disconnect in postman real quickly to try exit in the middle of the get_or_create action

[Errors]

Traceback (most recent call last):
  File "/home/yuzixin/workspace/sanicserver/venv/lib/python3.10/site-packages/tortoise/models.py", line 1057, in get_or_create
    await cls.select_for_update().filter(**kwargs).using_db(connection).get(),
  File "/home/yuzixin/workspace/sanicserver/venv/lib/python3.10/site-packages/tortoise/queryset.py", line 1006, in _execute
    instance_list = await self._db.executor_class(
  File "/home/yuzixin/workspace/sanicserver/venv/lib/python3.10/site-packages/tortoise/backends/base/executor.py", line 130, in execute_select
    _, raw_results = await self.db.execute_query(query.get_sql())
  File "/home/yuzixin/workspace/sanicserver/venv/lib/python3.10/site-packages/tortoise/backends/mysql/client.py", line 44, in translate_exceptions_
    return await func(self, *args)
  File "/home/yuzixin/workspace/sanicserver/venv/lib/python3.10/site-packages/tortoise/backends/mysql/client.py", line 199, in execute_query
    await cursor.execute(query, values)
  File "/home/yuzixin/workspace/sanicserver/venv/lib/python3.10/site-packages/aiomysql/cursors.py", line 239, in execute
    await self._query(query)
  File "/home/yuzixin/workspace/sanicserver/venv/lib/python3.10/site-packages/aiomysql/cursors.py", line 457, in _query
    await conn.query(q)
  File "/home/yuzixin/workspace/sanicserver/venv/lib/python3.10/site-packages/aiomysql/connection.py", line 469, in query
    await self._read_query_result(unbuffered=unbuffered)
  File "/home/yuzixin/workspace/sanicserver/venv/lib/python3.10/site-packages/aiomysql/connection.py", line 672, in _read_query_result
    await result.read()
  File "/home/yuzixin/workspace/sanicserver/venv/lib/python3.10/site-packages/aiomysql/connection.py", line 1153, in read
    first_packet = await self.connection._read_packet()
  File "/home/yuzixin/workspace/sanicserver/venv/lib/python3.10/site-packages/aiomysql/connection.py", line 598, in _read_packet
    packet_header = await self._read_bytes(4)
  File "/home/yuzixin/workspace/sanicserver/venv/lib/python3.10/site-packages/aiomysql/connection.py", line 646, in _read_bytes
    data = await self._reader.readexactly(num_bytes)
  File "/home/yuzixin/usr/lib/python3.10/asyncio/streams.py", line 708, in readexactly
    await self._wait_for_data('readexactly')
  File "/home/yuzixin/usr/lib/python3.10/asyncio/streams.py", line 502, in _wait_for_data
    await self._waiter
asyncio.exceptions.CancelledError

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/yuzixin/workspace/sanicserver/venv/lib/python3.10/site-packages/sanic/app.py", line 994, in _websocket_handler
    await fut
  File "/home/yuzixin/workspace/sanicserver/filesystem/blueprint.py", line 19, in feed
    await Room.get_or_create(channel_name='test_channel')
  File "/home/yuzixin/workspace/sanicserver/venv/lib/python3.10/site-packages/tortoise/models.py", line 1054, in get_or_create
    async with in_transaction(connection_name=db.connection_name) as connection:
  File "/home/yuzixin/workspace/sanicserver/venv/lib/python3.10/site-packages/tortoise/backends/base/client.py", line 280, in __aexit__
    await self.connection.rollback()
  File "/home/yuzixin/workspace/sanicserver/venv/lib/python3.10/site-packages/tortoise/backends/mysql/client.py", line 255, in rollback
    await self._connection.rollback()
  File "/home/yuzixin/workspace/sanicserver/venv/lib/python3.10/site-packages/aiomysql/connection.py", line 398, in rollback
    await self._execute_command(COMMAND.COM_QUERY, "ROLLBACK")
  File "/home/yuzixin/workspace/sanicserver/venv/lib/python3.10/site-packages/aiomysql/connection.py", line 695, in _execute_command
    self._ensure_alive()
  File "/home/yuzixin/workspace/sanicserver/venv/lib/python3.10/site-packages/aiomysql/connection.py", line 1114, in _ensure_alive
    raise InterfaceError(self._close_reason)
pymysql.err.InterfaceError: Cancelled during execution

Error at shutting down the server (a cold shutdown, as the warm shutdown would take forever)

Process ForkProcess-4:
Traceback (most recent call last):
  File "/home/yuzixin/usr/lib/python3.10/multiprocessing/process.py", line 315, in _bootstrap
    self.run()
  File "/home/yuzixin/usr/lib/python3.10/multiprocessing/process.py", line 108, in run
    self._target(*self._args, **self._kwargs)
  File "/home/yuzixin/workspace/sanicserver/venv/lib/python3.10/site-packages/sanic/server/runners.py", line 191, in serve
    loop.run_until_complete(app._server_event("shutdown", "after"))
  File "uvloop/loop.pyx", line 1499, in uvloop.loop.Loop.run_until_complete
RuntimeError: Event loop stopped before Future completed.

Same error occurs in __aenter__ as well, depending on the timing disconnection is triggered.

I tried adding a simple try except logic to __aexit__ at line 279 and 281, tortoise/backends/base/client.py, simply passing the exception and it is not blocking the server loop anymore. I am not an expert on async programming, but I feel like this might not be a final solution.

I was actually hoping this situation rarely occurs, as it looks like "trying to close mysql connection after ensure_connection but before the next several lines of code". But as I observed, this happened once every two tries

Expected behavior
Correctly closing the task in the middle of a transaction

Start with tortoise/backends/base/client.py, especially the transaction context manager's aenter and aexit paths shown in the traceback. Reproduce cancellation during Room.get_or_create in the MySQL-backed websocket example, then check that transaction cleanup and server shutdown complete without the rollback or event-loop errors described.