[BUILD] Build break in OLTP_FILE tests

[marcalff]

Fixes #2658

Changes

Please provide a brief description of the changes here.

• Add an explicit dependency to nlohmann_json in test otlp_file_client_test.
• This is required to build with non standard install locations.

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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.57%. Comparing base (497eaf4) to head (a408c4e).
Report is 59 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2659      +/-   ##
==========================================
+ Coverage   87.12%   87.57%   +0.46%     
==========================================
  Files         200      188      -12     
  Lines        6109     5848     -261     
==========================================
- Hits         5322     5121     -201     
+ Misses        787      727      -60     

see 55 files with indirect coverage changes