CI: Fix file structure of the notarized app bundle

Apparently this is a common mistake when using
ditto. The `--keepParent` flag should keep the
topmost folder in the archive as well, so it can
be properly notarized.

.github/actions/sign-godot-project/macos/sign.sh

@@ -40,7 +40,7 @@ codesign --verify "${app_path}"
 
 echo "Archiving and notarizing the signed app..."
 
-ditto -ck "${app_path}" "${archive_path}"
+ditto -ck --keepParent "${app_path}" "${archive_path}"
 xcrun notarytool submit "${archive_path}" --apple-id ${apple_dev_id} --team-id ${apple_dev_team_id} --password ${apple_dev_password} --wait
 
 echo "Stapling the notarization ticket to the signed app..."