### 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_terrain_peering_bit", "peering_bit", "terrain"), &TileData::set_terrain_peering_bit);
	ClassDB::bind_method(D_METHOD("get_terrain_peering_bit", "peering_bit"), &TileData::get_terrain_peering_bit);
	
	ClassDB::bind_method(D_METHOD("set_navigation_polygon", "layer_id", "navigation_polygon"), &TileData::set_navigation_polygon);
	ClassDB::bind_method(D_METHOD("get_navigation_polygon", "layer_id"), &TileData::get_navigation_polygon);
	
	ClassDB::bind_method(D_METHOD("set_probability", "probability"), &TileData::set_probability);
	ClassDB::bind_method(D_METHOD("get_probability"), &TileData::get_probability);
	
	ClassDB::bind_method(D_METHOD("set_custom_data", "layer_name", "value"), &TileData::set_custom_data);
	ClassDB::bind_method(D_METHOD("get_custom_data", "layer_name"), &TileData::get_custom_data);
	ClassDB::bind_method(D_METHOD("set_custom_data_by_layer_id", "layer_id", "value"), &TileData::set_custom_data_by_layer_id);
	ClassDB::bind_method(D_METHOD("get_custom_data_by_layer_id", "layer_id"), &TileData::get_custom_data_by_layer_id);
	ADD_GROUP("Rendering", "");
	ADD_PROPERTY(PropertyInfo(Variant::BOOL, "flip_h"), "set_flip_h", "get_flip_h");
	ADD_PROPERTY(PropertyInfo(Variant::BOOL, "flip_v"), "set_flip_v", "get_flip_v");
	ADD_PROPERTY(PropertyInfo(Variant::BOOL, "transpose"), "set_transpose", "get_transpose");
	ADD_PROPERTY(PropertyInfo(Variant::VECTOR2I, "texture_origin", PROPERTY_HINT_NONE, "suffix:px"), "set_texture_origin", "get_texture_origin");
	ADD_PROPERTY(PropertyInfo(Variant::COLOR, "modulate"), "set_modulate", "get_modulate");
	ADD_PROPERTY(PropertyInfo(Variant::OBJECT, "material", PROPERTY_HINT_RESOURCE_TYPE, "CanvasItemMaterial,ShaderMaterial"), "set_material", "get_material");
	ADD_PROPERTY(PropertyInfo(Variant::INT, "z_index"), "set_z_index", "get_z_index");
	ADD_PROPERTY(PropertyInfo(Variant::INT, "y_sort_origin"), "set_y_sort_origin", "get_y_sort_origin");
	ADD_GROUP("Terrains", "");
	ADD_PROPERTY(PropertyInfo(Variant::INT, "terrain_set"), "set_terrain_set", "get_terrain_set");
	ADD_PROPERTY(PropertyInfo(Variant::INT, "terrain"), "set_terrain", "get_terrain");
	ADD_GROUP("Miscellaneous", "");
	ADD_PROPERTY(PropertyInfo(Variant::FLOAT, "probability"), "set_probability", "get_probability");
	ADD_SIGNAL(MethodInfo("changed"));
}