test (validations) : Add some unit tests around proxy validation (#4411)

[rohanKanojia]

Description

Fixes: #4411

Relates to: An internal conversation related to validation error on Podman Desktop

Add some unit tests to test various values provided to these validation methods:

• validateHTTPProxy
• validateHTTPSProxy
• validateNoProxy

Type of change

• Bug fix (non-breaking change which fixes an issue)
• Feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change
• Chore (non-breaking change which doesn't affect codebase;
  test, version modification, documentation, etc.)

Proposed changes

Add some unit test cases for proxy validation.

Testing

N/A

Contribution Checklist

• I Keep It Small and Simple: The smaller the PR is, the easier it is to review and have it merged
• I have performed a self-review of my code
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Which platform have you tested the code changes on?
  • Linux
  • Windows
  • MacOS

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