Merge pull request #26590 from Kumataro:fix26589

Support C++20 standard #26590

Close https://github.com/opencv/opencv/issues/26589
Related https://github.com/opencv/opencv_contrib/pull/3842
Related: https://github.com/opencv/opencv/issues/20269

- do not arithmetic enums and ( different enums or floating numeric) 
- remove unused variable

### Pull Request Readiness Checklist

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

- [x] I agree to contribute to the project under Apache 2 License.
- [x] 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
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work
- [x] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [x] The feature is well documented and sample code can be built with the project CMake

modules/photo/src/calibrate.cpp

@@ -228,7 +228,7 @@ public:
 
         dst.create(LDR_SIZE, 1, CV_32FCC);
         Mat response = dst.getMat();
-        response = linearResponse(3) / (LDR_SIZE / 2.0f);
+        response = linearResponse(3) / (static_cast<float>(LDR_SIZE) / 2.0f);
 
         Mat card = Mat::zeros(LDR_SIZE, 1, CV_32FCC);
         for(size_t i = 0; i < images.size(); i++) {

modules/photo/src/merge.cpp

@@ -338,7 +338,7 @@ public:
 
         Mat response = input_response.getMat();
         if(response.empty()) {
-            float middle = LDR_SIZE / 2.0f;
+            float middle = static_cast<float>(LDR_SIZE) / 2.0f;
             response = linearResponse(channels) / middle;
         }
         CV_Assert(response.rows == LDR_SIZE && response.cols == 1 &&