`IndexFile._to_relative_path` - fix case where absolute path gets stripped of trailing slash by kamilkozik7 · Pull Request #2012

`IndexFile._to_relative_path` - fix case where absolute path gets stripped of trailing slash by kamilkozik7 · Pull Request #2012 · gitpython-developers/GitPython

I encountered this issue on MacOS, python 3.7 and later

Added fix and appropriate unit test.

Stripping of trailing slash seems to be happening in os.path.relpath, altough I am not sure whether that is expected behaviour. In case it is not expected, and ever gets fixed, I added an additional check ( and not result.endswith(os.sep)) to make sure that the trailing slash doesn't get duplicated.