[Internal] Unified Terraform Provider: BugFix for Notebook Data source (#5173)

## Changes
<!-- Summary of your changes that are easy to understand -->
Newly generated DatabricksClient is only for resources / data sources
not using Go SDK. This data source has some parts some are using Go SDK
and some which don't.

We would have proper fix to prevent this by adding a marker in the newly
Generated DatabricksClient which would prevent usage of these clients by
other methods. This would first need a change internally. Will create
this in a separate PR.

## Tests
<!--
How is this tested? Please see the checklist below and also describe any
other relevant tests
-->
CI Tests
NO_CHANGELOG=true

Author: tanmay-db

workspace/data_notebook.go

@@ -56,15 +56,15 @@ func DataSourceNotebook() common.Resource {
 	return common.Resource{
 		Schema: s,
 		Read: func(ctx context.Context, d *schema.ResourceData, m *common.DatabricksClient) error {
-			m, err := m.DatabricksClientForUnifiedProvider(ctx, d)
+			newClient, err := m.DatabricksClientForUnifiedProvider(ctx, d)
 			if err != nil {
 				return err
 			}
 			w, err := m.WorkspaceClientUnifiedProvider(ctx, d)
 			if err != nil {
 				return err
 			}
-			notebooksAPI := NewNotebooksAPI(ctx, m)
+			notebooksAPI := NewNotebooksAPI(ctx, newClient)
 			path := d.Get("path").(string)
 			format := d.Get("format").(string)
 			notebookContent, err := notebooksAPI.Export(path, format)