Fix skip-ci on `stable`. #128

Job	Run time
Check for 'skip-ci' label	1s
check-msrv	1m 56s
check-code	2m 18s
target-branch-check	0s
release-tests-windows	0s
op-pool-tests	0s
release-tests-ubuntu	0s
beacon-chain-tests	0s
debug-tests-ubuntu	0s
network-tests	0s
slasher-tests	0s
state-transition-vectors-ubuntu	0s
basic-simulator-ubuntu	0s
ef-tests-ubuntu	0s
fallback-simulator-ubuntu	0s
cargo-udeps	0s
cli-check	0s
compile-with-beta-compiler	0s
execution-engine-integration-ubuntu	0s
test-suite-success	1s
	4m 16s

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