I'm wondering if it would be worth having a testing tag targeting the testing repo. Sort of like the devel tag, but using the testing repo instead of latest release, and perhaps setting the usual ENVs to rolling.

# setup sources.list
- RUN echo "deb http://packages.ros.org/ros2/ubuntu `lsb_release -sc` main" &gt; /etc/apt/sources.list.d/ros2-latest.list<br class="Apple-interchange-newline">
+ RUN echo "deb http://packages.ros.org/ros2-testing/ubuntu `lsb_release -sc` main" &gt; /etc/apt/sources.list.d/ros2-testing.list<br class="Apple-interchange-newline">

Hmm, well, I guess more like nightly but without installing rolling from the fat archive or nurfing rosdistro.

We'd probably want to revisit how to keep these images up-to-date.
I think we could use a similar pattern that I've used for Nav2, but add pip update and such:

https://github.com/ros-planning/navigation2/blob/22407b7522b4b07cc65a0c3ab865aa4dc7c34282/.github/workflows/trigger_dockerhub.yaml#L22-L32

CC @mikaelarguedas @nuclearsandwich