dashboard/app/app.yaml: go122 -> go123 #15435

Job	Run time
dashboard	2m 40s
build	4m 33s
arch (presubmit_arch_linux)	9m 4s
aux	4m 27s
old	6m 15s
arch (presubmit_arch_freebsd)	5m 33s
race	4m 45s
arch (presubmit_arch_netbsd)	3m 35s
arch (presubmit_arch_openbsd)	3m 27s
race_dashboard	2m 59s
arch (presubmit_arch_darwin)	3m 24s
arch (presubmit_arch_windows)	3m 17s
gvisor	3m 12s
arch (presubmit_arch_executor)	3m 6s
	1h 0m 17s

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