Migrating to deb822 sources on upgrade to Mantic

[Nick Rosbrook]

Hi,

As a part of the effort to use deb822 sources by default in Ubuntu[1],
on upgrades to Mantic, ubuntu-release-upgrader will migrate
/etc/apt/sources.list to /etc/apt/sources.list.d/ubuntu.sources, and
/etc/apt/sources.list.d/foo.list to
/etc/apt/sources.list.d/foo.sources. This change has been implemented
and is now in mantic.

Please report any bugs you encounter.

Thanks,
Nick

[1] https://discourse.ubuntu.com/t/spec-apt-deb822-sources-by-default/29333