ci: run a mingw64 job on stable Fedora

ci: run a mingw64 job on stable Fedora

Both of the current mingw jobs are marked as 'allow_failure' because
they are running against Fedora rawhide which is an unstable distro.

We need at least one mingw job to be gating to more reliably detect
problems.

This introduces dockerfiles for both mingw variants on Fedora 35
and sets the mingw64 build to run on Fedora 34, and mingw32 on
Fedora rawhide.

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>