Tile Line brush starting cell gizmo is offset if the grid cell size is not uniform

Steps to reproduce:

1. Open the attached project
2. Open the SampleScene
3. Select the Grid object and verify that the Grid cell size is uniform
4. Select a tile from the TilePalette window and set the brush mode to Line
5. Click on the Tilemap
6. Observe that a blue gizmo is correctly set at the beginning of the line
7. Set the Grid's Y Cell size to 0.5
8. Repeat steps 4 and 5

Actual results: The blue gizmo indicating the starting cell of the line is offset

Expected results: The blue gizmo indicating the starting cell of the line is not offset

Reproducible with versions: 6000.0.74f1, 6000.3.15f1, 6000.4.5f1, 6000.5.0b6, 6000.6.0a4

Tested on (OS): Windows 11, macOS 26.4.1