### 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 allow_transform;
}
TileData *TileData::duplicate() {
	TileData *output = memnew(TileData);
	output->tile_set = tile_set;
	output->allow_transform = allow_transform;
	
	output->flip_h = flip_h;
	output->flip_v = flip_v;
	output->transpose = transpose;
	output->texture_origin = texture_origin;
	output->material = material;
	output->modulate = modulate;
	output->z_index = z_index;
	output->y_sort_origin = y_sort_origin;
	output->occluders = occluders;
	
	output->physics = physics;
	
	output->terrain_set = -1;
	memcpy(output->terrain_peering_bits, terrain_peering_bits, 16 * sizeof(int));
	
	output->navigation = navigation;
	
	output->probability = probability;
	
	output->custom_data = custom_data;
	return output;
}
void TileData::set_flip_h(bool p_flip_h) {