der_derive: add workaround for `syn` v2.0.73 #1323

Job	Run time
build (1.65.0, thumbv7em-none-eabi)	2m 14s
test (1.65.0)	2m 32s
build (1.65.0, wasm32-unknown-unknown)	2m 16s
test (stable)	27s
build (stable, thumbv7em-none-eabi)	20s
build (stable, wasm32-unknown-unknown)	16s
minimal-versions / minimal-versions	32s
	8m 37s

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