der: fix CI config for path to `der_derive` (#1460) #1181

Job	Run time
build (1.75.0, thumbv7em-none-eabi)	21s
build (1.75.0, wasm32-unknown-unknown)	26s
build (stable, thumbv7em-none-eabi)	10s
build (stable, wasm32-unknown-unknown)	11s
minimal-versions	0s
test (1.75.0)	30s
test (stable)	24s
	2m 2s

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