windows-server guest os doesn't mount unattended.iso

**I confirm this bug has not already been reported** - [x] I have searched the issues and this bug has not been reported previously **Describe the bug** When `guest_os` is marked as `windows-server` instead of `windows`, `unattended.iso` is not mounted, which breaks unattended installation of windows server unless it's disguised as `windows`. **To Reproduce** See above. **Expected behaviour** `unattended.iso` should be mounted the same way it's mounted for `windows` guest. **Quickemu output** N/A **System information** N/A **Screenshots** N/A **Additional context** N/A