Fix py38 tests

[balloob]

Breaking change

Proposed change

Fix all tests that broke under 3.8 in #34654 that I could locally reproduce.

Digging into core tests now.

It's either a timing issue (add a block till done) or some edge cases when mocking coroutines. Getting rid of mock_coro and using patch from asynctest fixes it.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

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# Example configuration.yaml

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• This PR fixes or closes issue: fixes #
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Checklist

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[probot-home-assistant]

Hey there @robbiet480, @Kane610, mind taking a look at this pull request as its been labeled with a integration (zeroconf) you are listed as a codeowner for? Thanks!

[probot-home-assistant]

Hey there @home-assistant/cloud, mind taking a look at this pull request as its been labeled with a integration (google_assistant) you are listed as a codeowner for? Thanks!