dashboard/app: fix up pprof handlers access #18478

Job	Run time
dashboard	2m 43s
race	7m 8s
gvisor	4m 5s
old	7m 7s
aux	3m 57s
build	5m 47s
arch (presubmit_arch_executor)	3m 17s
arch (presubmit_arch_linux)	10m 37s
arch (presubmit_arch_darwin)	3m 43s
arch (presubmit_arch_freebsd)	6m 26s
arch (presubmit_arch_netbsd)	3m 49s
arch (presubmit_arch_openbsd)	3m 30s
arch (presubmit_arch_windows)	3m 31s
race_dashboard	2m 47s
	1h 8m 27s

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