### 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)

ERR_FAIL_INDEX(p_layer_id, physics.size());
	ERR_FAIL_INDEX(p_polygon_index, physics[p_layer_id].polygons.size());
	physics.write[p_layer_id].polygons.remove_at(p_polygon_index);
	emit_signal(SNAME("changed"));
}
void TileData::set_collision_polygon_points(int p_layer_id, int p_polygon_index, Vector<Vector2> p_polygon) {
	ERR_FAIL_INDEX(p_layer_id, physics.size());
	ERR_FAIL_INDEX(p_polygon_index, physics[p_layer_id].polygons.size());
	ERR_FAIL_COND_MSG(p_polygon.size() != 0 && p_polygon.size() < 3, "Invalid polygon. Needs either 0 or more than 3 points.");
	if (p_polygon.is_empty()) {
		physics.write[p_layer_id].polygons.write[p_polygon_index].shapes.clear();
	} else {
		
		Vector<Vector<Vector2>> decomp = Geometry2D::decompose_polygon_in_convex(p_polygon);
		ERR_FAIL_COND_MSG(decomp.is_empty(), "Could not decompose the polygon into convex shapes.");
		physics.write[p_layer_id].polygons.write[p_polygon_index].shapes.resize(decomp.size());
		for (int i = 0; i < decomp.size(); i++) {
			Ref<ConvexPolygonShape2D> shape;
			shape.instantiate();
			shape->set_points(decomp[i]);
			physics.write[p_layer_id].polygons.write[p_polygon_index].shapes[i] = shape;
		}
	}
	physics.write[p_layer_id].polygons.write[p_polygon_index].polygon = p_polygon;
	emit_signal(SNAME("changed"));
}
Vector<Vector2> TileData::get_collision_polygon_points(int p_layer_id, int p_polygon_index) const {