CI: test `ctutils` using `cargo miri` #58

Job	Run time
test-miri (x86_64-unknown-linux-gnu)	40s
test-careful	57s
test (stable)	11s
test-miri (s390x-unknown-linux-gnu)	55s
build (stable, thumbv7em-none-eabi)	16s
build (1.85.0, wasm32-unknown-unknown)	17s
minimal-versions / minimal-versions	28s
test (1.85.0)	15s
build (stable, wasm32-unknown-unknown)	14s
build (1.85.0, thumbv7em-none-eabi)	15s
	4m 28s

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