zeroize_derive: fixup test suite [1.4] #1065

Job	Run time
cross (powerpc-unknown-linux-gnu, 1.56.0)	5m 51s
aarch64 (aarch64-unknown-linux-gnu, stable)	47s
aarch64 (aarch64-unknown-linux-gnu, 1.59.0)	5m 58s
cross (powerpc-unknown-linux-gnu, stable)	31s
build (stable, thumbv7em-none-eabi)	10s
build (1.56.0, armv7a-none-eabi)	5m 42s
build (stable, wasm32-unknown-unknown)	14s
minimal-versions / minimal-versions	39s
build (1.56.0, thumbv7em-none-eabi)	5m 34s
test (x86_64-pc-windows-msvc, windows-latest, 1.56.0)	6m 2s
test (x86_64-unknown-linux-gnu, ubuntu-latest, stable)	21s
test (x86_64-apple-darwin, macos-latest, 1.56.0)	6m 0s
build (1.56.0, wasm32-unknown-unknown)	5m 20s
test (x86_64-apple-darwin, macos-latest, stable)	25s
test (i686-unknown-linux-gnu, ubuntu-latest, 1.56.0, sudo apt update && sudo apt install gcc-mult...	4m 27s
test (i686-unknown-linux-gnu, ubuntu-latest, stable, sudo apt update && sudo apt install gcc-mult...	48s
test (x86_64-unknown-linux-gnu, ubuntu-latest, 1.56.0)	3m 34s
build (stable, armv7a-none-eabi)	14s
test (x86_64-pc-windows-msvc, windows-latest, stable)	1m 5s
	53m 42s

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