alpha channel always added to tiff export
GIMP version: 2.10.12
Operating System: opensuse 15.1
Package: official suse package
Description of the bug
Whenever I open an image (e.g. pgm or tiff) without an alpha channel and then export it to tiff, an alpha channel will unknowingly be added. There is no indication that an alpha channel or transparent layer is present in that image. When I open the exported image again, gimp shows me that it has an alpha channel. Gimp 2.8 doesn't do that.