PYTHON-4731 - Explicitly close all MongoClients opened during tests #534

Job	Run time
Make SDist	33s
Build wheels for manylinux_x86_64	2m 37s
Build wheels for manylinux_aarch64	10m 28s
Build wheels for manylinux_ppc64le	9m 40s
Build wheels for manylinux_s390x	10m 6s
Build wheels for manylinux_i686	2m 28s
Build wheels for win_amd6	5m 12s
Build wheels for win32	5m 19s
Build wheels for macos	3m 36s
Download Wheels	7s
	50m 6s

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