Minor discrepancy between --set spec.rootVolume.type and InstanceGroup `spec.rootVolumeType`

/kind bug

**1. What `kops` version are you running? The command `kops version`, will display
this information.**

Client version: 1.33.1 (git-v1.33.1)

**2. What Kubernetes version are you running? `kubectl version` will print the
version if a cluster is running or provide the Kubernetes version specified as
a `kops` flag.**

**3. What cloud provider are you using?**

**4. What commands did you run? What is the simplest way to reproduce this issue?**

Used `kops edit instancegroup --set spec.rootVolume.type=VALUE`, however when text editing using `kops edit instancegroup` it is shown as `spec.rootVolumeType`

**5. What happened after the commands executed?**

**6. What did you expect to happen?**

Expected the value to be shown in InstanceGroup as `spec.rootVolume.type`.

**7. Please provide your cluster manifest. Execute
`kops get --name my.example.com -o yaml` to display your cluster manifest.
You may want to remove your cluster name and other sensitive information.**

```yaml
```

**8. Please run the commands with most verbose logging by adding the `-v 10` flag.
Paste the logs into this report, or in a gist and provide the gist link here.**

**9. Anything else do we need to know?**

Start with the `kops edit instancegroup --set spec.rootVolume.type=VALUE` and `kops edit instancegroup` entry points, then trace how the root-volume field is parsed and rendered. Reproduce the discrepancy with both commands and verify that the same value is represented consistently as `spec.rootVolume.type`.

Written by the indexing model from the issue text.