[Fix] mws workspaces mishandling empty response

[VenelinMartinov]

Changes

This PR fixes the databricks_mws_workspaces datasource to correctly return an empty list when no mws workspaces are configured. It would previously return a nil, which caused certain Terraform programs to misbehave.

For example this would error instead of correctly returning 0:

data "databricks_mws_workspaces" "example" {}

output "workspace_ids" {
  value = data.databricks_mws_workspaces.example.ids
}

output "workspace_count" {
  value = length(data.databricks_mws_workspaces.example.ids)
}

Tests

I've added a test similar to the existing tests for the mws_workspaces data source

[github-actions]

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Trigger:
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Inputs:

• PR number: 4414
• Commit SHA: 9e9c8d9b3a921b98e6317c9a9e488e0648fd5d1f

Checks will be approved automatically on success.

[alexott]

lgtm