newvm: Adjust min memory for Fedora 41+

The Anaconda runtime is _way_ bigger in Fedora 41, presumably
because of the new web UI.  Even though we use text-only automated
installs, we still need enough space for the whole thing to fit in RAM.

newvm.sh

@@ -138,6 +138,11 @@ if [ -z "${LIBVIRT_DEFAULT_URI}" ]; then
     exit 1
 fi
 
+if [ ${fedora} -gt 40 ] && [ ${memory} -lt 4096 ]; then
+    printf 'WARNING Fedora 41+ requires at least 4 GB memory to install\n' >&2
+    memory=4096
+fi
+
 if ${default_groups}; then
     groups_xml="<group name=\"chrony\"/>${groups_xml}"
     groups_xml="<group name=\"collectd\"/>${groups_xml}"