pkg/aflow: add explicit DoWhile.MaxIterations #19162

Job	Run time
old	7m 6s
race	7m 6s
gvisor	4m 7s
race_dashboard	3m 5s
build	4m 16s
aux	3m 56s
arch (presubmit_arch_windows)	3m 38s
arch (presubmit_arch_openbsd)	3m 48s
arch (presubmit_arch_darwin)	3m 51s
arch (presubmit_arch_freebsd)	6m 25s
dashboard	2m 47s
arch (presubmit_arch_linux)	10m 36s
arch (presubmit_arch_executor)	3m 21s
arch (presubmit_arch_netbsd)	3m 53s
	1h 7m 55s

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