[Doc] Clarify workspace provider config

[ryan-gord-db]

Changes

Specifying the account_id field within a workspace provider block may cause an error when creating workspace resources (e.g. #3495). This change explicitly calls out this misconfiguration in the docs.

Tests

• [ ] make test run locally
• [x] 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: 4208
• Commit SHA: 0493af745260fbda0580b7ca978b3c25a8bb23b3

Checks will be approved automatically on success.

[eng-dev-ecosystem-bot]

Test Details: go/deco-tests/11803143386