Actually, I have no idea why this happened.
In my repo the file is absolutely safe: https://github.com/f-morozov/opencv/tree/for_pr/doc/tutorials/bioinspired/retina_model
But still this commit shows, that it should be empty: https://github.com/f-morozov/opencv/commit/a581c74728a464ad907c789b83829695edb9d0cf
How do I fix this?