test: Update Elastic test secret configuration

[tippmar-nr]

Updates elastic test configuration to reference Elastic8. Works in conjunction with a github secrets update I just pushed and is needed in order for the Elastic / OTel bridge PR to run tests against Elastic 9

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.21%. Comparing base (b45aca5) to head (e6a23a7).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3193      +/-   ##
==========================================
+ Coverage   82.18%   82.21%   +0.02%     
==========================================
  Files         487      487              
  Lines       31203    31203              
  Branches     3555     3555              
==========================================
+ Hits        25644    25653       +9     
+ Misses       4734     4723      -11     
- Partials      825      827       +2     

Flag	Coverage Δ
Agent	83.47% <ø> (+0.03%)	⬆️
Profiler	70.33% <ø> (ø)

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see 3 files with indirect coverage changes

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