### 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)

Vector<String> components = String(p_name).split("/", true, 2);
	if (components.size() >= 2 && components[0] == "scenes" && components[1].is_valid_int() && scenes.has(components[1].to_int())) {
		if (components.size() >= 3 && components[2] == "scene") {
			r_ret = scenes[components[1].to_int()].scene;
			return true;
		} else if (components.size() >= 3 && components[2] == "display_placeholder") {
			r_ret = scenes[components[1].to_int()].scene;
			return true;
		}
	}
	return false;
}
void TileSetScenesCollectionSource::_get_property_list(List<PropertyInfo> *p_list) const {