[INSTALL] Fix cmake/opentelemetry-cpp-config.cmake.in

[marcalff]

Fixes # (issue)

Changes

Please provide a brief description of the changes here.

• Fix broken test introduced by [EXPORTER] Allow to share gRPC clients between OTLP exporters #3041

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[netlify]

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[marcalff]

@owent Please review.

[marcalff]

This is a regression, blocking the 1.18.0 release.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.86%. Comparing base (9d998e3) to head (5fbc927).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3165   +/-   ##
=======================================
  Coverage   87.86%   87.86%           
=======================================
  Files         195      195           
  Lines        6151     6151           
=======================================
  Hits         5404     5404           
  Misses        747      747           

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