Tests

fix EthersDB deadlock #2658

Job	Run time
check no-default-features	24s
check serde	22s
check std	20s
clippy	1m 5s
test stable --no-default-features	48s
test no_std	22s
test stable	47s
test stable --all-features	1m 2s
test beta --no-default-features	46s
test beta	47s
test beta --all-features	1m 5s
fmt	11s
test nightly --no-default-features	44s
docs	1m 14s
test nightly	51s
test nightly --all-features	59s
	11m 47s

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