It seems the zip that is generated when using -z doesn't have the modified addon.xml. I guess the issue might be in the util.create_zip method, since the uploaded PR is modified fine.
Example: https://github.com/enen92/screensaver.kaster/releases/tag/1.3.5
If you take a look at the matrix-zip, you'll notice that it doesn't contain the xbmc.python = 3.0.0 line.