Blender Git Loki

Fix T91808: Batch Generate Previews fails

Caused by the Cycles-X merge.

The old style of tile rendering was removed, leaving the script to error
out trying to set the tile size.

Tile rendering came back in a new form (but only really relevant for
large resolution rendering), so now leave setting auto_tile & tile_size
alone (since previews are rendered at PREVIEW_RENDER_DEFAULT_HEIGHT 128
-- which should never make a difference here).

Maniphest Tasks: T91808

Differential Revision: https://developer.blender.org/D12937