Fix iotlab sniffer/serial and collect experiments
Adapt code to changes in RolesLike structure. Manually tested running docs/tutorials/iotlab/tuto_iotlab_m3_radio_sniffer.py
GitLab upgrade completed. Current version is 18.3.6
https://about.gitlab.com/releases/2025/07/17/gitlab-18-2-released/
https://about.gitlab.com/releases/2025/08/21/gitlab-18-3-released/
Adapt code to changes in RolesLike structure. Manually tested running docs/tutorials/iotlab/tuto_iotlab_m3_radio_sniffer.py