tests/docker: bump fedora to 32

We should be keeping this up to date as Fedora goes out of support
quite quickly.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20200612190237.30436-2-alex.bennee@linaro.org>

tests/docker/dockerfiles/fedora.docker

-FROM fedora:30
+FROM fedora:32
 
 # Please keep this list sorted alphabetically
 ENV PACKAGES \