test: improve WPT runner summary #5168

Job	Run time
Build slim tarball	2m 8s
x86_64-linux: with shared libraries	3m 36s
aarch64-linux: with shared libraries	3m 36s
aarch64-darwin: with shared libraries	3m 38s
x86_64-darwin: with shared libraries	3m 43s
	16m 41s

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