### 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)

PropertyInfo property_info;
	for (const KeyValue<Vector2i, TileAlternativesData> &E_tile : tiles) {
		List<PropertyInfo> tile_property_list;
		
		property_info = PropertyInfo(Variant::VECTOR2I, "size_in_atlas", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_NO_EDITOR);
		if (E_tile.value.size_in_atlas == Vector2i(1, 1)) {
			property_info.usage ^= PROPERTY_USAGE_STORAGE;
		}
		tile_property_list.push_back(property_info);
		
		property_info = PropertyInfo(Variant::INT, "next_alternative_id", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_NO_EDITOR);
		if (E_tile.value.next_alternative_id == 1) {
			property_info.usage ^= PROPERTY_USAGE_STORAGE;
		}