digest: fixup imports for `hash_serialization_test` macro (#1537) #2025

Job	Run time
minimal-versions	46s
build (1.65.0, thumbv7em-none-eabi)	42s
test (1.65.0)	48s
build (1.65.0, wasm32-unknown-unknown)	42s
build (stable, thumbv7em-none-eabi)	10s
test (stable)	17s
build (stable, wasm32-unknown-unknown)	13s
	3m 38s

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