tests: Remove Ubuntu 20.04 container

Since Ubuntu 22.04 has now been available for more than two years, we
can stop actively supporting the previous LTS version of Ubuntu now.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20240418101056.302103-2-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
2 files changed