tools: make `v8.nix` more stable #4905

Job	Run time
Build slim tarball	2m 42s
aarch64-linux: with shared libraries	1h 21m 47s
aarch64-darwin: with shared libraries	1h 53m 41s
x86_64-linux: with shared libraries	1h 49m 53s
x86_64-darwin: with shared libraries	3h 31m 37s
	8h 39m 40s

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