PYTHON-5488 `append_metadata` should not add duplicates #2673

Job	Run time
Make SDist	33s
Build wheels for manylinux_x86_64	2m 27s
Build wheels for win32	5m 1s
Build wheels for win_amd6	5m 7s
Build wheels for macos	3m 32s
Build wheels for manylinux_aarch64	5m 36s
Build wheels for manylinux_i686	2m 37s
Build wheels for manylinux_s390x	5m 36s
Build wheels for manylinux_ppc64le	5m 36s
Download Wheels	1s
	36m 6s

Provide feedback