tests/docker: switch fedora image to release 35

The Fedora 33 release is shortly end of life. Switch to the newest
Fedora 35 to maximise lifespan until we need to update again.

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20211215141949.3512719-7-berrange@redhat.com>
Message-Id: <20220105135009.1584676-7-alex.bennee@linaro.org>

tests/docker/dockerfiles/fedora.docker

-FROM registry.fedoraproject.org/fedora:33
+FROM registry.fedoraproject.org/fedora:35
 
 # Please keep this list sorted alphabetically
 ENV PACKAGES \