dashboard/app: fix admin checks for dev_appserver #18481

Job	Run time
build	5m 17s
race	8m 56s
race_dashboard	3m 30s
gvisor	4m 8s
old	7m 3s
aux	3m 38s
dashboard	2m 31s
arch (presubmit_arch_openbsd)	3m 47s
arch (presubmit_arch_netbsd)	3m 53s
arch (presubmit_arch_linux)	10m 43s
arch (presubmit_arch_windows)	3m 33s
arch (presubmit_arch_freebsd)	6m 27s
arch (presubmit_arch_darwin)	3m 44s
arch (presubmit_arch_executor)	3m 15s
	1h 10m 25s

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