fix overflow tests #213

Job	Run time
check-code	13m 36s
beacon-chain-tests	1h 27m 39s
check-msrv	11m 17s
cargo-udeps	13m 7s
compile-with-beta-compiler	24m 2s
debug-tests-ubuntu	24m 36s
dockerfile-ubuntu	25m 26s
doppelganger-protection-test	44m 38s
ef-tests-ubuntu	1h 2m 57s
eth1-simulator-ubuntu	38m 17s
merge-transition-ubuntu	50m 21s
execution-engine-integration-ubuntu	23m 52s
network-tests	26m 32s
no-eth1-simulator-ubuntu	45m 30s
op-pool-tests	36m 19s
release-tests-ubuntu	1h 34m 14s
release-tests-windows	1h 54m 18s
slasher-tests	4m 48s
state-transition-vectors-ubuntu	15m 27s
target-branch-check	2s
syncing-simulator-ubuntu	43m 12s
	13h 20m 10s

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