### 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(p_layer_index, physics_layers.size());
	physics_layers.write[p_layer_index].collision_layer = p_layer;
	emit_changed();
}
uint32_t TileSet::get_physics_layer_collision_layer(int p_layer_index) const {
	ERR_FAIL_INDEX_V(p_layer_index, physics_layers.size(), 0);
	return physics_layers[p_layer_index].collision_layer;
}
void TileSet::set_physics_layer_collision_mask(int p_layer_index, uint32_t p_mask) {
	ERR_FAIL_INDEX(p_layer_index, physics_layers.size());
	physics_layers.write[p_layer_index].collision_mask = p_mask;
	emit_changed();
}
uint32_t TileSet::get_physics_layer_collision_mask(int p_layer_index) const {
	ERR_FAIL_INDEX_V(p_layer_index, physics_layers.size(), 0);
	return physics_layers[p_layer_index].collision_mask;
}
void TileSet::set_physics_layer_physics_material(int p_layer_index, Ref<PhysicsMaterial> p_physics_material) {
	ERR_FAIL_INDEX(p_layer_index, physics_layers.size());
	physics_layers.write[p_layer_index].physics_material = p_physics_material;
}
Ref<PhysicsMaterial> TileSet::get_physics_layer_physics_material(int p_layer_index) const {
	ERR_FAIL_INDEX_V(p_layer_index, physics_layers.size(), Ref<PhysicsMaterial>());
	return physics_layers[p_layer_index].physics_material;
}
int TileSet::get_terrain_sets_count() const {