test: allow skipping individual WPT subtests #5141

Job	Run time
Build slim tarball	2m 29s
x86_64-linux: with shared libraries	21m 36s
x86_64-darwin: with shared libraries	2m 10s
aarch64-linux: with shared libraries	18m 22s
aarch64-darwin: with shared libraries	18m 46s
	1h 3m 23s

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