dashboard/app: make static resources work for dev_appserver.py #18487

Job	Run time
race_dashboard	2m 36s
aux	4m 7s
race	7m 15s
build	4m 4s
dashboard	2m 45s
gvisor	4m 4s
arch (presubmit_arch_linux)	10m 36s
arch (presubmit_arch_freebsd)	6m 32s
arch (presubmit_arch_windows)	3m 39s
arch (presubmit_arch_executor)	3m 44s
old	7m 4s
arch (presubmit_arch_darwin)	3m 48s
arch (presubmit_arch_netbsd)	3m 52s
arch (presubmit_arch_openbsd)	4m 11s
	1h 8m 17s

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