PYTHON-5488 `append_metadata` should not add duplicates #2677

Job	Run time
Build wheels for manylinux_s390x	11m 31s
Build wheels for manylinux_x86_64	2m 20s
Build wheels for manylinux_ppc64le	10m 55s
Build wheels for macos	3m 34s
Build wheels for manylinux_aarch64	11m 20s
Build wheels for manylinux_i686	2m 25s
Build wheels for win32	5m 29s
Build wheels for win_amd6	4m 53s
Make SDist	31s
Download Wheels	7s
	53m 5s

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