This changes the deprecated :show-nested: instruction to the :nested: one [1]
Tentatively trying to fix failing build on master [2] to fix the failing build on doc [3]
[1] https://sphinx-click.readthedocs.io/en/latest/usage/#directive-click
[2] https://jenkins.softwareheritage.org/job/DFUSE/job/tests/723/consolex
[3] D7745, D7748