Use httptest server for running healthcheck tests

[jjngx]

Proposed changes

Resolves: #4431
Use server from the httptest pkg for running healtcheck tests.

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

[codecov]

Codecov Report

Merging #4461 (f78b1aa) into main (3e16b62) will decrease coverage by 0.12%.
The diff coverage is n/a.

❗ Current head f78b1aa differs from pull request most recent head c742e11. Consider uploading reports for the commit c742e11 to get more accurate results

@@            Coverage Diff             @@
##             main    #4461      +/-   ##
==========================================
- Coverage   52.08%   51.97%   -0.12%     
==========================================
  Files          59       59              
  Lines       16956    16956              
==========================================
- Hits         8832     8813      -19     
- Misses       7825     7848      +23     
+ Partials      299      295       -4     

see 2 files with indirect coverage changes

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