macos template: "A software update is required to complete the installation" but no update is available

### Description

with lima 2.1.1 installed on macbook pro running Tahoe 26.3.1, the command `limactl create template:macos` (or `limactl start template:homebrew-macos`) produces the following error message:

```
FATA[0003] failed to install macOS: Error Domain=VZErrorDomain Code=10006 Description="A software update is required to complete the installation. Installation requires a software update." UserInfo={
NSLocalizedFailure = "A software update is required to complete the installation.";
NSLocalizedFailureReason = "Installation requires a software update.";
}
```

executing `sudo softwareupdate -l` produces the message:
```
No new software available.
```

Any idea what specific software needs to be updated, and what version is required?