fix missing metrics endpoint

[dtrifiro]

see vllm-project/vllm#6463

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 65.00000% with 7 lines in your changes missing coverage. Please review.

Project coverage is 63.03%. Comparing base (0b69d69) to head (c1565ec).

Files	Patch %	Lines
tests/conftest.py	41.66%	5 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main      #50       +/-   ##
===========================================
+ Coverage   31.45%   63.03%   +31.57%     
===========================================
  Files          18       18               
  Lines        1278     1285        +7     
  Branches      228      228               
===========================================
+ Hits          402      810      +408     
+ Misses        874      398      -476     
- Partials        2       77       +75     

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[dtrifiro]

Merge after #51