ubuntu.sources can become broken via GUI

[James Paton-Smith]

With the latest proposed versions of software-properties-gtk, software-properties-common, and python3-software-properties (0.99.44), it is possible to break the default ubuntu.sources list.

How to replicate
1. Open software-properties-gtk
2. Uncheck all of the repository suites (main, universe, multiverse, etc.)
3. Cat the /etc/apt/sources.list.d/ubuntu.sources file. It should be mostly empty.
4. Re-check all of the repository suites again.
5. Cat the /etc/apt/sources.list.d/ubuntu.sources file again. It will still be mostly empty with no repository configuration present.

The ubuntu.sources file remains in a broken state even though software-properties-gtk shows the suites as checked.

We can workaround this issue by using the 'Revert' button in software-properties-gtk.

ProblemType: Bug
DistroRelease: Ubuntu 24.04
Package: software-properties-gtk 0.99.44
ProcVersionSignature: Ubuntu 6.5.0-26.26-generic 6.5.13
Uname: Linux 6.5.0-26-generic x86_64
ApportVersion: 2.28.0-0ubuntu1
Architecture: amd64
CasperMD5CheckMismatches: ./boot/grub/grub.cfg
CasperMD5CheckResult: fail
CurrentDesktop: ubuntu:GNOME
Date: Fri Mar 22 09:05:37 2024
InstallationDate: Installed on 2024-03-13 (9 days ago)
InstallationMedia: Ubuntu 24.04 LTS "Noble Numbat" - Daily amd64 (20240313)
PackageArchitecture: all
ProcEnviron:
 LANG=en_GB.UTF-8
 PATH=(custom, no user)
 SHELL=/bin/bash
 TERM=xterm-256color
 XDG_RUNTIME_DIR=<set>
SourcePackage: software-properties
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.