tests/docker/dockerfiles: Bump fedora-i386-cross to fedora 34

For unknown and unrepeatable reasons, the cross-i386-tci test has
started failing.  "Fix" this by updating the container to use fedora 34.

Add sysprof-capture-devel as a new dependency of glib2-devel that
was not correctly spelled out in the rpm rules.

Use dnf update Just In Case -- there are presently out-of-date
packages in the upstream docker registry.

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20211005205846.153724-1-richard.henderson@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>