dashboard/app: fix admin checks for dev_appserver #18466

Job	Run time
race	1s
race_dashboard	1s
aux	1m 49s
gvisor	1m 49s
old	1m 53s
dashboard	1m 50s
arch (presubmit_arch_openbsd)	1m 47s
arch (presubmit_arch_linux)	1m 50s
arch (presubmit_arch_freebsd)	1m 50s
arch (presubmit_arch_executor)	1m 48s
arch (presubmit_arch_darwin)	1m 49s
arch (presubmit_arch_windows)	1m 49s
build	1s
arch (presubmit_arch_netbsd)	1m 49s
	20m 6s

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