Boot should fail instead of booting fallback OS

[lukasfrank]

What happened:
I created a ServerClaim with the following image ghcr.io/ironcore-dev/feos/feos:fix-oci-layout.
The server booted up correctly but with a different OS (GardenLinux)

What you expected to happen:
If something went wrong an error should be reported instead of booting up something else

[hardikdr]

The root cause of this behavior likely stems from the configuration. If the boot operator is started with both the HTTPBoot and IPXEBoot translators enabled, they may race to declare the ServerBootConfiguration as Ready, while the other may report an Error. This results in inconsistent feedback to the Metal operator, potentially causing it to proceed for the server boot.