Hypothesis for Python - version 6.15.0

This release emits a more useful error message when "@given()" is
applied to a coroutine function, i.e. one defined using "async def"
(issue #3054).

This was previously only handled by the generic "return_value" health
check, which doesn't direct you to use either a custom executor or a
library such as pytest-trio or pytest-asyncio to handle it for you.

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