Hello @hbigot,
OK, the problem is rather clear from the warning.
For whatever reason SonarQube is unable to detect the SCM used (Git/GitHub) when analyzing the code, and cannot retrieve all the pull request information (SCM revision) to decorate.
Normally this should be auto detected (simply by the presence of a .git directory in the root of your project after checkout in your CI or your local machine).
How do you checkout the code ? git clone/pull/fetch/checkout or something else ?