Do not treat security report schema validation warnings as errors - old

What does this MR do and why?

When verifying Validate security report schema using the lates... (#351519 - closed) using https://gitlab.com/gitlab-org/secure/tests/test-for-issue-351519 it came to our attention that the logic wouldn't work as expect only by modifying the schema validator – https://gitlab.com/gitlab-org/secure/tests/test-for-issue-351519/-/pipelines/614397738/security

This MR makes the common security report parser treat warnings as warnings instead of errors depending on the validate flag.

Related to #351519 (closed)

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