[docs] asyncio.Semaphore.release is not a coroutine

[Alexander Shorin]

Hi docs@ team!

Basically, asyncio.Semaphore.release method has a coroutine prefix in docs:
https://docs.python.org/3/library/asyncio-sync.html#asyncio.Semaphore.release

But in the code it has not such wrapper:
https://hg.python.org/cpython/file/b4cbecbc0781/Lib/asyncio/locks.py#l431

The exact type of .release() method is very important as coroutines
cannot be used in Future's on done callbacks and according
documentation it's not possible to do with Semaphore.release while
it's not a true.

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