der: deprecate `ErrorKind::SetDuplicate` (#2276) #3606

Job	Run time
build (1.85.0, wasm32-unknown-unknown)	25s
test (stable)	51s
build (1.85.0, thumbv7em-none-eabi)	22s
test (1.85.0)	50s
build (stable, thumbv7em-none-eabi)	25s
build (stable, wasm32-unknown-unknown)	21s
minimal-versions / minimal-versions	35s
	3m 49s

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