fix tests in signer crate #43

Job	Run time
doctest	28s
cfg-check	21s
clippy	15s
docs	25s
fmt	12s
no-std	10s
feature-checks	28s
test ubuntu-latest stable --no-default-features	1m 36s
wasm-wasi	1m 0s
wasm-unknown	18s
test ubuntu-latest stable	1m 39s
test ubuntu-latest nightly --no-default-features	1m 30s
test ubuntu-latest nightly	1m 28s
test ubuntu-latest 1.76 --no-default-features	27s
test ubuntu-latest 1.76	35s
test windows-latest stable --no-default-features	4m 51s
test windows-latest stable	4m 19s
test windows-latest nightly --no-default-features	3m 18s
test windows-latest nightly	2m 48s
test windows-latest 1.76 --no-default-features	2m 6s
test windows-latest 1.76	1m 54s
test ubuntu-latest stable --all-features	41s
test ubuntu-latest nightly --all-features	45s
	31m 34s

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