test: adapt buffer test for v8 sandbox #3288

Job	Run time
Build slim tarball	2m 44s
x86_64-linux: with shared libraries	49m 8s
aarch64-darwin: with shared libraries	55m 19s
x86_64-darwin: with shared libraries	1h 19m 30s
aarch64-linux: with shared libraries	39m 47s
	3h 46m 28s

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