Fix navmap_rviz_plugin build with Qt5 rviz_common and Qt6 installed - #44

Unexpected input(s) 'colcon-mixin-name', valid inputs are ['colcon-defaults', 'colcon-mixin-repository', 'coverage-result', 'coverage-ignore-pattern', 'extra-cmake-args', 'colcon-extra-args', 'import-token', 'package-name', 'target-ros1-distro', 'target-ros2-distro', 'vcs-repo-file-url', 'skip-tests', 'skip-rosdep-install', 'no-symlink-install', 'rosdep-check', 'rosdep-skip-keys', 'ref', 'git-ssh-port']