Mark test_distribution/test_layout_map_mesh_shapes as multi_device

test_layout_map_live_presets was the only test in this file carrying
@pytest.mark.multi_device, but it's also marked kaggle_key_required and
extra_large, so PR keras-team#2809's CI job (which filters on
"multi_device and not kaggle_key_required and not extra_large") was
excluding it too -- leaving zero real tests collected from this model.

Mark the two actual multi-device tests instead: test_distribution, and
test_layout_map_mesh_shapes (the Tier-2 CI-safe mesh-shape sweep).

For test_layout_map_mesh_shapes, the marker must go directly above the
def, below @parameterized.named_parameters, not above it: absl's
TestGeneratorMetaclass only forwards attributes set via functools.wraps
inside _ParameterizedTestIter.__iter__ on the original function; a mark
applied outermost lands on the _ParameterizedTestIter object itself and
is silently dropped when the class dict is rewritten, so none of the
12 expanded per-mesh-shape test cases would inherit it. Verified via
collect-only with the same "-m" filter CI uses: 13/19 tests selected
(test_distribution + 12 mesh-shape cases), with test_layout_map_live_presets
and the non-distribution tests correctly excluded either way.

Author: pctablet505

keras_hub/src/models/mixtral/mixtral_backbone_test.py

@@ -193,6 +193,7 @@ def test_num_parameters(self):
         )
         self.assertEqual(model.count_params(), expected_params)
 
+    @pytest.mark.multi_device
     def test_distribution(self):
         # num_experts=4, top_k=2 (distribution-test-only override, not the
         # shared setUp): with the shared setUp's num_experts=2, top_k=2,
@@ -253,6 +254,7 @@ def test_distribution(self):
         for dims in (MIXTRAL_SMALL_DIMS, MIXTRAL_BASE_DIMS)
         for shape in CAPPED_MESH_SHAPES
     )
+    @pytest.mark.multi_device
     def test_layout_map_mesh_shapes(self, dims, mesh_shape):
         if keras.backend.backend() != "jax":
             self.skipTest("`ModelParallel` testing requires the Jax backend.")