PYTHON-5488 `append_metadata` should not add duplicates #2674

Job	Run time
Make SDist	42s
Build wheels for manylinux_aarch64	11m 30s
Build wheels for manylinux_x86_64	2m 29s
Build wheels for manylinux_i686	2m 37s
Build wheels for win32	4m 47s
Build wheels for manylinux_ppc64le	11m 7s
Build wheels for win_amd6	4m 25s
Build wheels for macos	4m 35s
Build wheels for manylinux_s390x	11m 27s
Download Wheels	8s
	53m 47s

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