Add CPE match API tests + small fixes

[timopollmeier]

What

Tests are added for the CPE match API, matchCriteriaId is converted to a string for HTTP requests and cpe_last_modified of CPE matches is made optional

Why

The tests were originally omitted from the PR that added the API.

References

GEA-790

Checklist

• Tests

[github-actions]

Conventional Commits Report

Type	Number
Bug Fixes	2
Added	1

🚀 Conventional commits found.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.31%. Comparing base (721a24b) to head (55e5552).
Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1074      +/-   ##
==========================================
+ Coverage   89.92%   90.31%   +0.38%     
==========================================
  Files         108      108              
  Lines        7187     7187              
  Branches      815      815              
==========================================
+ Hits         6463     6491      +28     
+ Misses        521      491      -30     
- Partials      203      205       +2     

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