der: fix CI config for path to `der_derive` (#1460) #1872

Job	Run time
build (1.65.0, thumbv7em-none-eabi)	2m 6s
build (1.65.0, wasm32-unknown-unknown)	2m 8s
build (stable, thumbv7em-none-eabi)	24s
build (stable, wasm32-unknown-unknown)	23s
test (1.65.0)	2m 15s
test (stable)	19s
minimal-versions / minimal-versions	26s
	8m 1s

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