tests/avocado: Replace assertEquals() for Python 3.12 compatibility

assertEquals() has been removed in Python 3.12 and should be replaced by
assertEqual(). See: https://docs.python.org/3.12/whatsnew/3.12.html#id3



Message-ID: <20231114134326.287242-1-thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>