Add session migration for GNOME 42 dark theme

[Jeremy Bícha]

Test Case
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1. From Ubuntu 20.04 LTS or 21.10, open the Settings app. Click Appearance and choose Dark
2. Upgrade to Ubuntu 22.04 LTS
3. Log out then log back in
4. Your apps should still be dark

Linked Issue
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That test case is broken by the libhandy update. See LP: #1964841

We are updating gnome-control-center to set the correct gsettings value (below) when choosing a dark theme.

Workaround
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If you want the fix to apply without logging out at any time, you can run
session-migration --file /usr/share/session-migration/scripts/dark-theme-migration.sh

This requires gsettings-desktop-schemas 42~rc-1ubuntu3 or higher

Or you can run this command yourself instead
gsettings set org.gnome.desktop.interface color-scheme 'prefer-dark'

[Jeremy Bícha (jbicha)]

Since it's gsettings-desktop-schemas that provides the new schema, Seb suggested we just add the migration there directly. Thanks!

[Launchpad Janitor (janitor)]

This bug was fixed in the package gsettings-desktop-schemas - 42~rc-1ubuntu3

---------------
gsettings-desktop-schemas (42~rc-1ubuntu3) jammy; urgency=medium

  * Add dark-theme migration script using dh-migrations (LP: #1965189)

 -- Jeremy Bicha <email address hidden> Thu, 17 Mar 2022 09:49:43 -0400