sec1

der: add Set_of_ref struct #4569

Job	Run time
build (1.85.0, thumbv7em-none-eabi)	37s
test (stable)	1m 13s
build (stable, wasm32-unknown-unknown)	39s
build (1.85.0, wasm32-unknown-unknown)	42s
test (1.85.0)	1m 22s
build (stable, thumbv7em-none-eabi)	41s
minimal-versions / minimal-versions	41s
	5m 55s

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