dashboard/app: fix total coverage visualization #14745

Job	Run time
dashboard	3m 27s
aux	4m 47s
build	10m 48s
arch (presubmit_arch_linux)	10m 55s
gvisor	4m 9s
old	6m 30s
arch (presubmit_arch_freebsd)	6m 36s
race	8m 39s
arch (presubmit_arch_netbsd)	4m 26s
arch (presubmit_arch_openbsd)	4m 24s
race_dashboard	4m 17s
arch (presubmit_arch_darwin)	4m 23s
arch (presubmit_arch_windows)	3m 25s
arch (presubmit_arch_executor)	3m 18s
	1h 20m 4s

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