Fix tests for OTEL 1.28.1

[alexmojaki]

Following #583 (comment)

It looks like by default exemplars shouldn't be created for measurements made outside of the context of a trace.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (1353ed7) to head (3eddb23).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #594   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files          133       133           
  Lines        10441     10441           
  Branches      1427      1427           
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  Hits         10441     10441           

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