rospack: 2.1.23-0 in 'groovy/distribution.yaml' [bloom]

Increasing version of package(s) in repository `rospack` to `2.1.23-0`:

- distro file: `groovy/distribution.yaml`
- bloom version: `0.5.1`
- previous version for package: `2.1.21-1`

## rospack

```
* only perform backquote substitution when needed (#34 <https://github.com/ros/rospack/issues/34>)
```