koord-manager: fix the prom metrics handler

[saintube]

Ⅰ. Describe what this PR does

Ⅱ. Does this pull request fix one issue?

fixes #2105

Ⅲ. Describe how to verify it

Ⅳ. Special notes for reviews

V. Checklist

• I have written necessary docs and comments
• I have added necessary unit tests and integration tests
• All checks passed in make test

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.70%. Comparing base (6f1debb) to head (61f229a).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2107      +/-   ##
==========================================
- Coverage   68.71%   68.70%   -0.01%     
==========================================
  Files         430      430              
  Lines       40125    40125              
==========================================
- Hits        27570    27569       -1     
  Misses      10192    10192              
- Partials     2363     2364       +1     

Flag	Coverage Δ
unittests	68.70% <ø> (-0.01%)	⬇️

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[zwzhang0107]

/lgtm
/approve

[koordinator-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hormes, zwzhang0107

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