fixed possible FPs for some GCP instances checks when 'true' is capitalized

[halfluke]

Description

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Sorry, I am not sure what this is...

During a GCP assessment, I noticed that SS was reporting some false positives for "block project-wide ssh keys".
I identified the problem in the fact that in the GCP project, some values were reported in capital "TRUE", while SS only checks for "true". Code fixed to handle both cases, also for "OS login enabled" and "serial port enabled", just in case.

Fixes # (issue)
I don't think there is an open issue for this.

Type of change

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• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works (optional)
• New and existing unit tests pass locally with my changes