pkg/aflow: add explicit DoWhile.MaxIterations #19164

Job	Run time
race_dashboard	3m 7s
race	7m 25s
old	7m 10s
aux	3m 45s
dashboard	2m 41s
arch (presubmit_arch_freebsd)	5m 52s
gvisor	4m 3s
arch (presubmit_arch_linux)	11m 6s
arch (presubmit_arch_openbsd)	3m 50s
arch (presubmit_arch_darwin)	3m 49s
arch (presubmit_arch_executor)	3m 20s
build	4m 12s
arch (presubmit_arch_netbsd)	3m 59s
arch (presubmit_arch_windows)	3m 17s
	1h 7m 36s

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