test_extractor: Allow compile-only unittests for certain version's

[MoonlightSentinel]

This enables e.g. verification for tests hidden by version (StdDoc)
without running them (wich usually are version'ed for exactly that
reason).

This change wraps the unittest body in if (false) { ... } if it's
located within a version passed via --compileOnlyVersions.

CC @CyberShadow Opted for a different flag because both behaviours have their merit.

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[CyberShadow]

Honestly I feel like we are over-engineering this. It would have been simpler to just come up with a different test :)