### 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)

points.push_back(Vector2(-0.5, 0.0));
		points.push_back(Vector2(0.0, 0.5));
		points.push_back(Vector2(0.5, 0.0));
	} else {
		float overlap = 0.0;
		switch (tile_shape) {
			case TileSet::TILE_SHAPE_HEXAGON:
				overlap = 0.25;
				break;
			case TileSet::TILE_SHAPE_HALF_OFFSET_SQUARE:
				overlap = 0.0;
				break;
			default:
				break;
		}
		points.push_back(Vector2(0.0, -0.5));
		points.push_back(Vector2(-0.5, overlap - 0.5));
		points.push_back(Vector2(-0.5, 0.5 - overlap));
		points.push_back(Vector2(0.0, 0.5));
		points.push_back(Vector2(0.5, 0.5 - overlap));
		points.push_back(Vector2(0.5, overlap - 0.5));
		if (get_tile_offset_axis() == TileSet::TILE_OFFSET_AXIS_VERTICAL) {
			for (int i = 0; i < points.size(); i++) {
				points.write[i] = Vector2(points[i].y, points[i].x);
			}
		}
	}
	return points;
}
void TileSet::draw_tile_shape(CanvasItem *p_canvas_item, Transform2D p_transform, Color p_color, bool p_filled, Ref<Texture2D> p_texture) {