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

Truediv (floating point division) operators on line 149 of the tutorial produce floating point result:

crow,ccol = rows/2 , cols/2

Hence, indexing operation on line 153:

mask[crow-30:crow+30, ccol-30:ccol+30] = 1

Fails with an error:

TypeError: slice indices must be integers or None or have an __index__ method

This PR fixes the error by replacing the operators with floordiv (integer division) ones.