Per conversation with padillon , confidential compute clusters on Azure will not be able to use marketplace images. We should add a carveout for these clusters so that they are skipped for boot image updates(examine SecuritySettings fields within MachineSet objects to detect these cases). We should also make a mention of this limitation in the 4.21 docs. 

Additional context: https://issues.redhat.com/browse/CORS-4199?focusedId=28488703&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-28488703 

https://redhat-internal.slack.com/archives/C999USB0D/p1763539984234609?thread_ts=1763463924.768479&cid=C999USB0D