[issue47104] Rewrite asyncio.to_thread tests to use IsolatedAsyncioTestCase

[miss-islington]

Change by miss-islington <mariatta.wijaya+miss-islington at gmail.com>:


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pull_requests: +30175
pull_request: https://github.com/python/cpython/pull/32088

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue47104>
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