Description:

This PR resolves a warning caused by an unused variable IMAGE_BIKES in the file test_rotation_and_scale_invariance.cpp within the xfeatures2d module of the OpenCV contrib repository.

• Issue: The variable IMAGE_BIKES was declared but not used in the test file, leading to a compiler warning (-Wunused-const-variable).

warning: unused variable 'IMAGE_BIKES' [-Wunused-const-variable]
static const char* const IMAGE_BIKES = "detectors_descriptors_evaluation/

Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

• I agree to contribute to the project under Apache 2 License.
• To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
• The PR is proposed to the proper branch
• There is a reference to the original bug report and related work
• There is accuracy test, performance test and test data in opencv_extra repository, if applicable
  Patch to opencv_extra has the same branch name.
• The feature is well documented and sample code can be built with the project CMake