Add doesn't consider USER directives so use --chown flag.

ros_buildfarm/templates/doc/rosdoc2_task.Dockerfile.em

@@ -43,8 +43,8 @@ RUN echo "@today_str"
 
 RUN python3 -u /tmp/wrapper_scripts/apt.py update-install-clean -q -y -o Debug::pkgProblemResolver=yes build-essential python3-catkin-pkg-modules doxygen graphviz openssh-client python3 python3-yaml python3-pip rsync
 
+COPY --chown=@uid:@uid rosdoc2 /tmp/rosdoc2
 USER buildfarm
-COPY rosdoc2 /tmp/rosdoc2
 ENTRYPOINT ["sh", "-c"]
 @{
 cmd = 'PYTHONPATH=/tmp/ros_buildfarm:$PYTHONPATH python3 -u' + \