### Godot version

5ee983188de97ae027f9b9c1443438063f708a7e

### System information

Windows 11

### Issue description

Godot editor will throw an error and fail to generate preview icons for terrain tiles which use a base image which is not RGBA8 format.
`core\io\image.cpp:2788 - Condition "format != p_src->format" is true.`

### Steps to reproduce

- Import a non-RGBA8 image into Godot.
- Create a TileMap
- Create an associated TileSet
- Create a terrain for this tileset
- Add the image as an atlas
- Go to the paint tab
- Paint the terrain on the TileSet
- An error will occur any time terrains are edited in the TileSet editor or selected in the TileMap editor terrain tab.

### Minimal reproduction project

[tileset_terrain_bug.zip](https://github.com/godotengine/godot/files/13264213/tileset_terrain_bug.zip)

}
					}
				}
				
				if (!compatibility_size_count.has(ctd->region.get_size())) {
					compatibility_size_count[ctd->autotile_tile_size] = 0;
				}
				compatibility_size_count[ctd->autotile_tile_size] += atlas_size.x * atlas_size.y;
			} break;
		}
		
		for (int k = 0; k < ctd->shapes.size(); k++) {
			Ref<ConvexPolygonShape2D> convex = ctd->shapes[k].shape;
			if (convex.is_valid()) {
				Vector<Vector2> points = convex->get_points();
				for (int i_point = 0; i_point < points.size(); i_point++) {
					points.write[i_point] = points[i_point] - get_tile_size() / 2;
				}
				convex->set_points(points);
			}
		}
	}
	
	Vector2i max_size = get_tile_size();
	int max_count = 0;
	for (KeyValue<Vector2i, int> kv : compatibility_size_count) {
		if (kv.value > max_count) {