Do not treat security report schema validation warnings as errors

What does this MR do and why?

This MR makes the common security report parser treat warnings as warnings instead of errors. If the validate flag is set to false then we don't perform the validation at all

Related to #351519 (closed)

Run jsonlint on security report fixtures (!97806 - merged) should be merged before this one as it runs jsonlint on the schemas so they're more human-readable

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