test: migrate account deletion sync tests to testcontainers

[YB0y]

Summary

Migrate tests from api/tests/unit_tests/services/enterprise/test_account_deletion_sync.py
to testcontainers integration tests at
api/tests/test_containers_integration_tests/services/enterprise/test_account_deletion_sync.py.

All 11 tests migrated. DB-dependent tests (sync_account_deletion with multiple workspaces, no workspaces, partial/all failures) now use real PostgreSQL with TenantAccountJoin records instead of mocking db.session. The _queue_task success test uses real Redis to verify task payload. Redis error/type error tests and dify_config.ENTERPRISE_ENABLED remain mocked. Deleted the unit test file.

Part of #32454

Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues.
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran make lint and make type-check (backend) and cd web && npx lint-staged (frontend) to appease the lint gods

[github-actions]

Pyrefly Diff

No changes detected.

[github-actions]

Pyrefly Diff

No changes detected.

[asukaminato0721]

you can run ruff check --fix to speed up the ci.