Change RHEL-9 ur exclusion justification (#295)

Signed-off-by: Chris Lalancette <[email protected]>

rolling/release-rhel-build.yaml

@@ -56,7 +56,7 @@ package_blacklist:
 - sol_vendor  # Targets 'HEAD' in vendor package
 - tracetools_analysis  # jupyter-notebook has no RPM package for RHEL
 - tvm_vendor  # Build failures on AlmaLinux (but not RHEL)
-- ur_dashboard_msgs  # docker.io has no RPM packages for RHEL
+- ur_dashboard_msgs  # Upstream for ur_robot_driver, for which docker.io has no RPM packages for RHEL
 - usb_cam  # v4l-utils has no RPM package for RHEL
 - vrpn_mocap  # Requires unreleased changes: https://github.com/vrpn/vrpn/pull/278
 - warehouse_ros_mongo  # mongodb has no RPM package for RHEL