Add UT for CS_DISABLE_LANGUAGE_VULNERABILITY_SCAN in trivy_spec.rb

What does this MR do?

Add testing for trivy.rb's handling of CS_DISABLE_LANGUAGE_VULNERABILITY_SCAN.

What are the relevant issue numbers?

Non OS packages are present in the CycloneDX SB... (gitlab-org/gitlab#435390) • Yasha Rise • 17.1

And the following MR: Add vuln-type parameter to CS Trivy SBOM scan (!3029 - merged) • Yasha Rise (this thread)

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated for GitLab EE, if necessary
• Documentation created/updated for this project, if necessary
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Job definition updated, if necessary
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  • Job definition example
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• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer