* Move linux-x64-flutter-gtk.zip to linux-x64-debug location.

linux-x64-flutter-gtk.zip is being uploaded twice to linux-x64-debug
and linux-x64 as part of making a soft transition to use linux-x64-debug
location. This PR starts using the copy inside linux-x64-debug to later
remove the duplicated upload.

* Also move arm64.

* Do not override output dir.