Add CI that tests with gz-physics

[scpeters]

Is your feature request related to a problem? Please describe.

Gazebo uses dartsim, but Gazebo currently only tests with released versions of dartsim, so any problems that cause Gazebo to break require urgent action and additional patch releases to fix things.

Describe the solution you'd like

From @jslee02 in gazebosim/gz-physics#662 (comment):

Would it be beneficial to set up tests on the dartsim/dart repo to identify any issues with the Gazebo integration?

Yes, I think CI in the dartsim/dart repo that builds the latest stable version of gz-physics against dart from source would be very helpful in identifying incompatibilities.

cc @j-rivero to continue our discussion here.

Describe alternatives you've considered

Continue with the status quo.

Additional context
Add any other context or screenshots about the feature request here.