fix: add proper self-signed cert tests (with proxy option rejectUnauthorized)

[shazron]

⚠️ needs new @adobe/aio-lib-test-proxy release with this PR: adobe/aio-lib-test-proxy#7

How Has This Been Tested?

• npm test

Types of changes

• 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 change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (458fe01) to head (72cb103).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master       #70   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            5         5           
  Lines          135       135           
  Branches        31        31           
=========================================
  Hits           135       135           

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