... so that OPENCV_CUSTOM_PACKAGE_INFO actually has full effect.

At the moment packages are generated (via cpack) with an invalid (by debian-standards) name. The version section of the name should at least start with the number and follow the pattern major:minor.patch-arch. at the moment the version string is set to the git-hash (which generates an invalid filename).
anyway, the real problem is that i can't even be fixed by using OPENCV_CUSTOM_PACKAGE_INFO because VCS_VERSION is used directly instead of assigning it to the CPACK_PACKAGE_VERSION and using that.
This pull request makes it possible to generate packages with debian conform names.

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