### 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)

property_info = PropertyInfo(Variant::OBJECT, vformat("navigation_layer_%d/%s", i, PNAME("polygon")), PROPERTY_HINT_RESOURCE_TYPE, "NavigationPolygon", PROPERTY_USAGE_DEFAULT);
			if (!navigation[i].is_valid()) {
				property_info.usage ^= PROPERTY_USAGE_STORAGE;
			}
			p_list->push_back(property_info);
		}
		
		p_list->push_back(PropertyInfo(Variant::NIL, GNAME("Custom Data", "custom_data_"), PROPERTY_HINT_NONE, "custom_data_", PROPERTY_USAGE_GROUP));
		for (int i = 0; i < custom_data.size(); i++) {
			Variant default_val;
			Callable::CallError error;
			Variant::construct(custom_data[i].get_type(), default_val, nullptr, 0, error);
			property_info = PropertyInfo(tile_set->get_custom_data_layer_type(i), vformat("custom_data_%d", i), PROPERTY_HINT_NONE, String(), PROPERTY_USAGE_DEFAULT | PROPERTY_USAGE_NIL_IS_VARIANT);
			if (custom_data[i] == default_val) {
				property_info.usage ^= PROPERTY_USAGE_STORAGE;
			}
			p_list->push_back(property_info);
		}
	}
}
void TileData::_bind_methods() {
	
	ClassDB::bind_method(D_METHOD("set_flip_h", "flip_h"), &TileData::set_flip_h);
	ClassDB::bind_method(D_METHOD("get_flip_h"), &TileData::get_flip_h);
	ClassDB::bind_method(D_METHOD("set_flip_v", "flip_v"), &TileData::set_flip_v);
	ClassDB::bind_method(D_METHOD("get_flip_v"), &TileData::get_flip_v);
	ClassDB::bind_method(D_METHOD("set_transpose", "transpose"), &TileData::set_transpose);
	ClassDB::bind_method(D_METHOD("get_transpose"), &TileData::get_transpose);
	ClassDB::bind_method(D_METHOD("set_material", "material"), &TileData::set_material);
	ClassDB::bind_method(D_METHOD("get_material"), &TileData::get_material);