Apps like Orca set X-GNOME-AutoRestart=true in their .desktop files
expecting to be restarted after a crash. However, the restart logic only
handled apps that registered as XSMP or D-Bus clients. Non-client apps
emitted "died"/"exited" signals but nothing subscribed to them. This bug
was inherited from gnome-session.

Connect the "died" and "exited" signals on autostart apps to trigger
restart for non-client apps with AutoRestart enabled. Also fall back to
X-GNOME-AutoRestart when X-MATE-AutoRestart is not present, for
compatibility with apps that only set the GNOME key.

Fixes #321

Adds optional libcanberra support to play desktop-login and
desktop-logout sound events during session start and end. Sound playback
is controlled through the system sound theme configuration.

Fixes #328

Bumps [actions/checkout](https://github.com/actions/checkout) from 5 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](https://github.com/actions/checkout/compare/v5...v6)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Replace Travis CI configuration with GitHub Actions workflows.
Add CI build workflow for Debian, Fedora, Ubuntu, and Archlinux.
Add release workflow for automated GitHub releases on tags.
Add dependabot configuration for GHA pin updates.
Remove obsolete .travis.yml.
remove .build.yml

This loosens mate-session's env var value restrictions to match
systemd's modern restrictions.

Backported from https://gitlab.gnome.org/GNOME/gnome-session/-/commit/cbc5e5de421359ee5642e44fa9ab670d705d23ea

It seems that the pattern we use will create a subpattern match for
every character of the value. This appears to then result in a stack
overflow when matching very long values.

It might be an idea to limit the overall length of an environment
variable that is uploaded. But, this should fix the issue of crashes.

Backported from https://gitlab.gnome.org/GNOME/gnome-session/-/commit/3b57d117f78ad06e56974b9512a394fd9ef13a07

Specifically, systemd only permits " \t\n" and we should stick to the
same set of permitted space characters.

See also
  https://github.com/systemd/systemd/issues/17378

Backported from https://gitlab.gnome.org/GNOME/gnome-session/-/commit/fe22c4ee12922d790478bfe8b5b2e7c1313ca2f0