Remove duplicate `ARRAY_CUSTOM_RGBA8_UNORM` ref in Mesh docs

[flooxo]

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This PR closes https://github.com/godotengine/godot-docs/issues/8901

Removes duplicate reference of ARRAY_CUSTOM_RGBA8_UNORM

[AThousandShips]

Looking at some of the code I think this should be ARRAY_CUSTOM_RGBA8_SNORM instead

CC @clayjohn

Not sure if this is the code for this but this seems relevant: https://github.com/godotengine/godot/blob/b4e2a24c1f62088b3f7ce0197afc90832fc25009/servers/rendering/renderer_rd/storage_rd/mesh_storage.cpp#L1298

[kleonc]

Looking at some of the code I think this should be ARRAY_CUSTOM_RGBA8_SNORM instead

Indeed, ArrayCustomFormat's docs already say it's one of the encoded as PackedByteArray formats: https://github.com/godotengine/godot/blob/36e943b6b20cb7a8a89bc30489c4a81c3e149d74/doc/classes/Mesh.xml#L264-L290

[AThousandShips]

Please edit your commit message to remove unnecessary messages from commits, should just say:

Remove duplicate reference of CUSTOM_ARRAY_RBGA8_URNOM in docs

[akien-mga]

Thanks! And congrats for your first merged Godot contribution :tada:

[akien-mga]

Cherry-picked for 4.2.2. Cherry-picked for 4.1.4.