If they create a signed app image with additional content passed through `--app-content`, the result app image can not be notarized.

If they create a signed app image with the same jpackage parameters without `--app-content`, copy the additional content into the app image, run codesign on it, and then notarization passes.

Clearly, this is not an issue with app content. Something is off with jpackage signing.

See https://github.com/openjdk/jdk/pull/21698#issuecomment-2847722058