syz-cluster: fix stats display for non finished sessions #17574

Job	Run time
build	3m 19s
aux	4m 33s
gvisor	3m 49s
dashboard	2m 22s
race_dashboard	3m 1s
race	8m 6s
arch (presubmit_arch_linux)	10m 26s
old	6m 59s
arch (presubmit_arch_openbsd)	3m 42s
arch (presubmit_arch_darwin)	3m 38s
arch (presubmit_arch_freebsd)	6m 13s
arch (presubmit_arch_netbsd)	3m 52s
arch (presubmit_arch_executor)	3m 17s
arch (presubmit_arch_windows)	3m 32s
	1h 6m 49s

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