Stop reading data_disk_type value from API response into state of google_notebooks_instance resource

[modular-magician]

Description

Fixes #8485

That issue linked above describes a permadiff/permadelete situation where:

• the Terraform config defines a type of disk to use in data_disk_type
• the notebook resource is created
• after creation, TF reads the resource from the API and overwrites state
• The API response doesn't include the data_disk_type value, so it is set to "" in state
• On the next plan TF identifies that the config has a non-zero value and the state has a zero value, so proposes a change
• The change is on a ForceNew field

This PR stops the data_disk_type value being read from the API to overwrite state.

This matches how the boot disk arguments are handled:

https://github.com/GoogleCloudPlatform/magic-modules/blob/ea34ac204ae9216682497593ad5e383a16585ff3/mmv1/products/notebooks/terraform.yaml#L70-L73

List

If this PR is for Terraform, I acknowledge that I have:

• Searched through the issue tracker for an open issue that this either resolves or contributes to, commented on it to claim it, and written "fixes {url}" or "part of {url}" in this PR description. If there were no relevant open issues, I opened one and commented that I would like to work on it (not necessary for very small changes).
• Generated Terraform, and ran make test and make lint to ensure it passes unit and linter tests.
• Ensured that all new fields I added that can be set by a user appear in at least one example (for generated resources) or third_party test (for handwritten resources or update tests). N/A
• Ran relevant acceptance tests (If the acceptance tests do not yet pass or you are unable to run them, please let your reviewer know).
  • Tests starting TestAccNotebooksInstance_ pass
• Read the Release Notes Guide before writing my release note below.

Release Note Template for Downstream PRs (will be copied)

notebooks: fixed perma-diff in `google_notebooks_instance`

Derived from GoogleCloudPlatform/magic-modules#6512

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