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

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

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

Inspired-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20231114144832.71612-1-philmd@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
(cherry picked from commit f0a663b4ced2bf315936c774c2b6ff398fce8905)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
(Mjt: adjust context for before v8.1.0-1582-g684750ab4f
 "python/qemu: rename command() to cmd()")