### 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)

return transpose;
}
void TileData::set_texture_origin(Vector2i p_texture_origin) {
	texture_origin = p_texture_origin;
	emit_signal(SNAME("changed"));
}
Vector2i TileData::get_texture_origin() const {
	return texture_origin;
}
void TileData::set_material(Ref<Material> p_material) {
	material = p_material;
	emit_signal(SNAME("changed"));
}
Ref<Material> TileData::get_material() const {
	return material;
}
void TileData::set_modulate(Color p_modulate) {
	modulate = p_modulate;
	emit_signal(SNAME("changed"));
}
Color TileData::get_modulate() const {
	return modulate;
}
void TileData::set_z_index(int p_z_index) {
	z_index = p_z_index;
	emit_signal(SNAME("changed"));
}
int TileData::get_z_index() const {