images: Move ubuntu-stable to noble devel series

The current devel series will become 24.04 LTS, thus a major/important
release again. Let's avoid repeating a regression catastrophe like 23.10
mantic, and start testing on it early, so that we have a chance to fix
up everything by the final release.

images/scripts/ubuntu-stable.bootstrap

@@ -15,4 +15,9 @@ fi
 # release name is the last part of the URL
 rel=${rel##*/}
 
+# noble will become 24.04 LTS, so let's test it before the release so that we can fix issues in time
+if [ "$rel" = "mantic" ]; then
+    rel="noble"
+ fi
+
 exec $(dirname $0)/lib/cloudimage.bootstrap "$1" "https://cloud-images.ubuntu.com/daily/server/$rel/current/$rel-server-cloudimg-amd64.img"