fix voronoi unit test in structures

Author: Jammy2211

autoarray/inversion/pixelization/image_mesh/overlay.py

@@ -220,11 +220,11 @@ def image_plane_mesh_grid_from(
             origin=origin,
         )
 
-        overlaid_centres = geometry_util.grid_pixel_centres_2d_slim_from(
+        overlaid_centres = np.array(geometry_util.grid_pixel_centres_2d_slim_from(
             grid_scaled_2d_slim=unmasked_overlay_grid,
             shape_native=mask.shape_native,
             pixel_scales=mask.pixel_scales,
-        ).astype("int")
+        )).astype("int")
 
         total_pixels = total_pixels_2d_from(
             mask_2d=mask.array,