Chore: ensure ducklake testing artifact is under a tmp path

[georgesittas]

The modified test currently leave an artifact behind, this PR fixes it:

((.venv) ) ➜  sqlmesh git:(main) ✗ pytest tests/core/engine_adapter/test_duckdb.py::test_ducklake_partitioning -vv
=================================================================================== test session starts ===================================================================================
platform darwin -- Python 3.12.10, pytest-8.3.5, pluggy-1.5.0 -- /sqlmesh/.venv/bin/python3.12
cachedir: .pytest_cache
rootdir: /sqlmesh
configfile: pyproject.toml
plugins: anyio-4.9.0, time-machine-2.16.0, retry-1.7.0, Faker-37.3.0, asyncio-0.26.0, mock-3.14.0, xdist-3.6.1
asyncio: mode=Mode.STRICT, asyncio_default_fixture_loop_scope=session, asyncio_default_test_loop_scope=function
collected 1 item

tests/core/engine_adapter/test_duckdb.py::test_ducklake_partitioning PASSED                                                                                                         [100%]

==================================================================================== warnings summary =====================================================================================
.venv/lib/python3.12/site-packages/astor/op_util.py:92
  /sqlmesh/.venv/lib/python3.12/site-packages/astor/op_util.py:92: DeprecationWarning: ast.Num is deprecated and will be removed in Python 3.14; use ast.Constant instead
    precedence_data = dict((getattr(ast, x, None), z) for x, y, z in op_data)

.venv/lib/python3.12/site-packages/pydantic/_internal/_generate_schema.py:293: 131 warnings
  /sqlmesh/.venv/lib/python3.12/site-packages/pydantic/_internal/_generate_schema.py:293: PydanticDeprecatedSince20: `json_encoders` is deprecated. See https://docs.pydantic.dev/2.11/concepts/serialization/#custom-serializers for alternatives. Deprecated in Pydantic V2.0 to be removed in V3.0. See Pydantic V2 Migration Guide at https://errors.pydantic.dev/2.11/migration/
    warnings.warn(

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
============================================================================= 1 passed, 132 warnings in 0.10s =============================================================================
((.venv) ) ➜  sqlmesh git:(main) ✗ gst
On branch main
Your branch is up to date with 'origin/main'.

Untracked files:
  (use "git add <file>..." to include in what will be committed)
    a_ducklake_db.ducklake

[treysp]

My bad - thank you for catching!