qemuxmlconftest: Prepare 'fd-memory-numa-topology4' for removal of 'pc-i440fx-5.0'

qemuxmlconftest: Prepare 'fd-memory-numa-topology4' for removal of 'pc-i440fx-5.0'

Per commit message of 3f390db2e2ed33cda8e which added the
'fd-memory-numa-topology4' case, it's supposed to test memory
preallocation setting in the NUMA setup.

Now the 5.0 machine type is the last one supporting the old-style NUMA
config and thus also the only way to test the formatting of
'--mem-prealloc' commandline option for qemu, which was since replaced
by a property in the memory backend object.

Thus to preserve the idea of this test, add
'fd-memory-numa-topology4-old-machine' test case pinned to qemu-10.2,
which will use pc-i440fx-5.0 and modernize the normal case using the
latest qemu version by dropping the specific machine version.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>