### 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)

ERR_FAIL_INDEX_V(p_layer_index, occlusion_layers.size(), 0);
	return occlusion_layers[p_layer_index].light_mask;
}
void TileSet::set_occlusion_layer_sdf_collision(int p_layer_index, bool p_sdf_collision) {
	ERR_FAIL_INDEX(p_layer_index, occlusion_layers.size());
	occlusion_layers.write[p_layer_index].sdf_collision = p_sdf_collision;
	emit_changed();
}
bool TileSet::get_occlusion_layer_sdf_collision(int p_layer_index) const {
	ERR_FAIL_INDEX_V(p_layer_index, occlusion_layers.size(), false);
	return occlusion_layers[p_layer_index].sdf_collision;
}
int TileSet::get_physics_layers_count() const {
	return physics_layers.size();
}
void TileSet::add_physics_layer(int p_index) {
	if (p_index < 0) {
		p_index = physics_layers.size();
	}
	ERR_FAIL_INDEX(p_index, physics_layers.size() + 1);
	physics_layers.insert(p_index, PhysicsLayer());
	for (KeyValue<int, Ref<TileSetSource>> source : sources) {
		source.value->add_physics_layer(p_index);
	}
	notify_property_list_changed();
	emit_changed();
}
void TileSet::move_physics_layer(int p_from_index, int p_to_pos) {