der: fix CI config for path to `der_derive` (#1460) #2332

Job	Run time
build (1.65.0, wasm32-unknown-unknown)	2m 19s
build (1.65.0, thumbv7em-none-eabi)	2m 21s
build (stable, wasm32-unknown-unknown)	32s
test (i686-unknown-linux-gnu, 1.65.0, sudo apt update && sudo apt install gcc-multilib)	6m 32s
build (stable, thumbv7em-none-eabi)	35s
test (i686-unknown-linux-gnu, stable, sudo apt update && sudo apt install gcc-multilib)	4m 14s
test (x86_64-unknown-linux-gnu, 1.65.0)	6m 30s
test (x86_64-unknown-linux-gnu, stable)	3m 57s
minimal-versions / minimal-versions	2m 21s
	29m 21s

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