### 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_COND(p_atlas_coords.x < 0 || p_atlas_coords.y < 0);
	ERR_FAIL_COND(p_size.x <= 0 || p_size.y <= 0);
	bool room_for_tile = has_room_for_tile(p_atlas_coords, p_size, 1, Vector2i(), 1);
	ERR_FAIL_COND_MSG(!room_for_tile, "Cannot create tile. The tile is outside the texture or tiles are already present in the space the tile would cover.");
	
	TileAlternativesData tad;
	tad.size_in_atlas = p_size;
	tad.animation_frames_durations.push_back(1.0);
	tad.alternatives[0] = memnew(TileData);
	tad.alternatives[0]->set_tile_set(tile_set);
	tad.alternatives[0]->set_allow_transform(false);
	tad.alternatives[0]->connect("changed", callable_mp((Resource *)this, &TileSetAtlasSource::emit_changed));
	tad.alternatives[0]->notify_property_list_changed();
	tad.alternatives_ids.push_back(0);
	
	tiles.insert(p_atlas_coords, tad);
	tiles_ids.push_back(p_atlas_coords);
	tiles_ids.sort();
	_create_coords_mapping_cache(p_atlas_coords);
	_queue_update_padded_texture();
	emit_signal(SNAME("changed"));
}
void TileSetAtlasSource::remove_tile(Vector2i p_atlas_coords) {