Restrict gnome & gnome-core to release architectures but

add loong64 and exclude i386 and armel

(My understanding is that i386 won't have Trixie install images either.)

I added loong64 since they are the only port to be up-to-date on GNOME Shell and the packageset has a reasonable chance of being installable in the future. They would need to figure out gtk4 first but maybe adding them to this task is helpful without causing other problems.

We need coordination with the Debian Release team to make this change: https://bugs.debian.org/1080521