Fix apriltag copy constructor test

[rolalaro]

• Fix a compilation warning when JSON is not available
• Fix copy constructor test of vpDetectorAprilTag in cathArUco

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 48.68%. Comparing base (b7b806c) to head (45fa18a).
⚠️ Report is 6 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1891      +/-   ##
==========================================
+ Coverage   48.62%   48.68%   +0.06%     
==========================================
  Files         532      532              
  Lines       69293    69293              
  Branches    32402    32403       +1     
==========================================
+ Hits        33691    33736      +45     
+ Misses      31477    31428      -49     
- Partials     4125     4129       +4     

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