PYTHON-4745 - Update Async Cancellation documentation #1635

Job	Run time
Build wheels for manylinux_x86_64	2m 21s
Make SDist	35s
Build wheels for manylinux_aarch64	11m 21s
Build wheels for manylinux_ppc64le	11m 0s
Build wheels for manylinux_s390x	11m 54s
Build wheels for manylinux_i686	2m 26s
Build wheels for win_amd6	5m 16s
Build wheels for win32	5m 48s
Build wheels for macos	4m 56s
Download Wheels	5s
	55m 42s

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