Catch concurrent.futures.CancelledError in websocket code.

[pelson]

Description:

It isn't clear why a concurrent.futures.CancelledError is appearing instead of an asyncio.CancelledError, but #9546 shows that it is (or at least, has done when the connection timed out).

Related issue (if applicable): fixes #9546.

Checklist:

• The code change is tested and works locally.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in home-assistant.github.io

If the code communicates with devices, web services, or third-party tools:

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass
• New dependencies have been added to the REQUIREMENTS variable (example).
• New dependencies are only imported inside functions that use them (example).
• New dependencies have been added to requirements_all.txt by running script/gen_requirements_all.py.
• New files were added to .coveragerc.

If the code does not interact with devices:

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass
• Tests have been added to verify that the new code works.

[pvizeli]

@balloob maybe we use future.CancelledError so that is clear to other one?

[balloob]

I agree with Pascal. Please do from concurrent import futures and please add a comment with a link to the issue for future reference.

I wonder if we should check this upstream to see if it has either been addressed already or is a known issue?

[balloob]

Awesome 👍