Add iron to Linux CI

[hoffmann-stefan]

Let's support Iron from day one :)

https://www.openrobotics.org/blog/2023/5/23/ros-2-iron-irwini-released

depends on update from ros-tooling/setup-ros:

• https://github.com/ros-tooling/setup-ros/pull/568

[hoffmann-stefan]

Let's support Iron from day one :)

Turned out to be day two ;)