der_derive: add workaround for `syn` v2.0.73 #699

Job	Run time
minimal-versions	0s
build (1.75.0, thumbv7em-none-eabi)	26s
build (1.75.0, wasm32-unknown-unknown)	24s
test (1.75.0)	30s
build (stable, thumbv7em-none-eabi)	25s
test (stable)	27s
build (stable, wasm32-unknown-unknown)	24s
	2m 36s

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