### 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)

ClassDB::bind_method(D_METHOD("set_texture_origin", "texture_origin"), &TileData::set_texture_origin);
	ClassDB::bind_method(D_METHOD("get_texture_origin"), &TileData::get_texture_origin);
	ClassDB::bind_method(D_METHOD("set_modulate", "modulate"), &TileData::set_modulate);
	ClassDB::bind_method(D_METHOD("get_modulate"), &TileData::get_modulate);
	ClassDB::bind_method(D_METHOD("set_z_index", "z_index"), &TileData::set_z_index);
	ClassDB::bind_method(D_METHOD("get_z_index"), &TileData::get_z_index);
	ClassDB::bind_method(D_METHOD("set_y_sort_origin", "y_sort_origin"), &TileData::set_y_sort_origin);
	ClassDB::bind_method(D_METHOD("get_y_sort_origin"), &TileData::get_y_sort_origin);
	ClassDB::bind_method(D_METHOD("set_occluder", "layer_id", "occluder_polygon"), &TileData::set_occluder);
	ClassDB::bind_method(D_METHOD("get_occluder", "layer_id"), &TileData::get_occluder);
	
	ClassDB::bind_method(D_METHOD("set_constant_linear_velocity", "layer_id", "velocity"), &TileData::set_constant_linear_velocity);
	ClassDB::bind_method(D_METHOD("get_constant_linear_velocity", "layer_id"), &TileData::get_constant_linear_velocity);
	ClassDB::bind_method(D_METHOD("set_constant_angular_velocity", "layer_id", "velocity"), &TileData::set_constant_angular_velocity);
	ClassDB::bind_method(D_METHOD("get_constant_angular_velocity", "layer_id"), &TileData::get_constant_angular_velocity);
	ClassDB::bind_method(D_METHOD("set_collision_polygons_count", "layer_id", "polygons_count"), &TileData::set_collision_polygons_count);
	ClassDB::bind_method(D_METHOD("get_collision_polygons_count", "layer_id"), &TileData::get_collision_polygons_count);
	ClassDB::bind_method(D_METHOD("add_collision_polygon", "layer_id"), &TileData::add_collision_polygon);
	ClassDB::bind_method(D_METHOD("remove_collision_polygon", "layer_id", "polygon_index"), &TileData::remove_collision_polygon);
	ClassDB::bind_method(D_METHOD("set_collision_polygon_points", "layer_id", "polygon_index", "polygon"), &TileData::set_collision_polygon_points);
	ClassDB::bind_method(D_METHOD("get_collision_polygon_points", "layer_id", "polygon_index"), &TileData::get_collision_polygon_points);
	ClassDB::bind_method(D_METHOD("set_collision_polygon_one_way", "layer_id", "polygon_index", "one_way"), &TileData::set_collision_polygon_one_way);
	ClassDB::bind_method(D_METHOD("is_collision_polygon_one_way", "layer_id", "polygon_index"), &TileData::is_collision_polygon_one_way);
	ClassDB::bind_method(D_METHOD("set_collision_polygon_one_way_margin", "layer_id", "polygon_index", "one_way_margin"), &TileData::set_collision_polygon_one_way_margin);
	ClassDB::bind_method(D_METHOD("get_collision_polygon_one_way_margin", "layer_id", "polygon_index"), &TileData::get_collision_polygon_one_way_margin);
	
	ClassDB::bind_method(D_METHOD("set_terrain_set", "terrain_set"), &TileData::set_terrain_set);
	ClassDB::bind_method(D_METHOD("get_terrain_set"), &TileData::get_terrain_set);
	ClassDB::bind_method(D_METHOD("set_terrain", "terrain"), &TileData::set_terrain);
	ClassDB::bind_method(D_METHOD("get_terrain"), &TileData::get_terrain);