Tests: Alembic: Add coverage for point cloud attribute import validation

Adds coverage for recently added import of pointcloud attributes.
See PR blender/blender!145946

Pull Request: https://projects.blender.org/blender/blender/pulls/147494

tests/python/CMakeLists.txt

@@ -1177,6 +1177,7 @@ if(WITH_ALEMBIC AND TEST_SRC_DIR_EXISTS)
     --python ${CMAKE_CURRENT_LIST_DIR}/bl_alembic_io_test.py
     --
     --testdir "${TEST_SRC_DIR}/alembic"
+    --outdir "${TEST_OUT_DIR}/io_alembic"
   )
 endif()