test: backfill auth test for OTEL_EXPORTER_OTLP_HEADERS

[codefromthecrypt]

Description

There is no issue, but we were missing tests for tracing and metrics authentication. This is needed for cloud environments like Elastic.

Related Issues/PRs (if applicable)

#1150

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.64%. Comparing base (9e9fba9) to head (d435e5a).

❌ Your project status has failed because the head coverage (79.64%) is below the target coverage (86.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1225      +/-   ##
==========================================
- Coverage   79.68%   79.64%   -0.04%     
==========================================
  Files          90       90              
  Lines       10247    10247              
==========================================
- Hits         8165     8161       -4     
- Misses       1719     1724       +5     
+ Partials      363      362       -1     

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