test: reduce waitForInitialBreak() flakiness in debugger tests #4007

Job	Run time
Build slim tarball	2m 0s
aarch64-linux: with shared libraries	19m 29s
x86_64-linux: with shared libraries	23m 7s
x86_64-darwin: with shared libraries	32m 45s
aarch64-darwin: with shared libraries	20m 34s
	1h 37m 55s

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