der_derive: add workaround for `syn` v2.0.73 #881

Job	Run time
test (1.75.0)	28s
build (1.75.0, thumbv7em-none-eabi)	22s
build (1.75.0, wasm32-unknown-unknown)	26s
test (stable)	25s
build (stable, thumbv7em-none-eabi)	22s
build (stable, wasm32-unknown-unknown)	26s
minimal-versions	0s
	2m 29s

Provide feedback