### 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 z_index;
}
void TileData::set_y_sort_origin(int p_y_sort_origin) {
	y_sort_origin = p_y_sort_origin;
	emit_signal(SNAME("changed"));
}
int TileData::get_y_sort_origin() const {
	return y_sort_origin;
}
void TileData::set_occluder(int p_layer_id, Ref<OccluderPolygon2D> p_occluder_polygon) {
	ERR_FAIL_INDEX(p_layer_id, occluders.size());
	occluders.write[p_layer_id] = p_occluder_polygon;
	emit_signal(SNAME("changed"));
}
Ref<OccluderPolygon2D> TileData::get_occluder(int p_layer_id) const {
	ERR_FAIL_INDEX_V(p_layer_id, occluders.size(), Ref<OccluderPolygon2D>());
	return occluders[p_layer_id];
}
void TileData::set_constant_linear_velocity(int p_layer_id, const Vector2 &p_velocity) {
	ERR_FAIL_INDEX(p_layer_id, physics.size());
	physics.write[p_layer_id].linear_velocity = p_velocity;
	emit_signal(SNAME("changed"));
}
Vector2 TileData::get_constant_linear_velocity(int p_layer_id) const {
	ERR_FAIL_INDEX_V(p_layer_id, physics.size(), Vector2());
	return physics[p_layer_id].linear_velocity;
}
void TileData::set_constant_angular_velocity(int p_layer_id, real_t p_velocity) {