Fix path replacement in codecov.yml

[christophfroehlich]

A minimum change since I fixed the workflow with ros-controls/ros2_control_ci#20

Already included in #53

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.90%. Comparing base (6b5d811) to head (ec49147).

Additional details and impacted files

@@             Coverage Diff             @@
##           master      #54       +/-   ##
===========================================
+ Coverage   39.34%   68.90%   +29.56%     
===========================================
  Files           2        3        +1     
  Lines         122      119        -3     
  Branches       64       64               
===========================================
+ Hits           48       82       +34     
  Misses         25       25               
+ Partials       49       12       -37     

Flag	Coverage Δ
unittests	68.90% <ø> (+29.56%)	⬆️

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see 3 files with indirect coverage changes