exec: avoid clobbering timeout #1816

Job	Run time
packages (arm64-secure, arm64)	5m 5s
packages (ubuntu-20.04, amd64)	5m 13s
packages (ubuntu-latest, riscv64)	3m 34s
verification (arm64, kvm)	12m 37s
verification (arm64, xen)	10m 41s
eve (arm64, kvm)	36m 6s
manifest	4m 48s
verification (amd64, kvm)	11m 31s
eve (arm64, xen)	35m 21s
verification (amd64, xen)	10m 1s
eve (amd64, kvm)	36m 1s
eve (amd64, xen)	36m 0s
eve (riscv64, mini)	6m 19s
	3h 33m 17s

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