[Fix] Always fill `cluster_name` in `databricks_cluster` data source

[alexott]

Changes

Tests

• [x] make test run locally
• [ ] relevant change in docs/ folder
• [ ] covered with integration tests in internal/acceptance
• [ ] relevant acceptance tests are passing
• [ ] using Go SDK

[github-actions[bot]]

If integration tests don't run automatically, an authorized user can run them manually by following the instructions below:

Trigger: go/deco-tests-run/terraform

Inputs:

• PR number: 4197
• Commit SHA: 745f268924c9c6730200b164eea607212e28e93e

Checks will be approved automatically on success.

[eng-dev-ecosystem-bot]

Test Details: go/deco-tests/11706980354