test: fix race condition in watch mode tests #2951

Job	Run time
Build slim tarball	1m 31s
x86_64-darwin: with shared libraries	1h 0m 10s
aarch64-linux: with shared libraries	1h 26m 27s
x86_64-linux: with shared libraries	2h 6m 14s
aarch64-darwin: with shared libraries	2h 12m 4s
	6h 46m 26s

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