Hi Sherrera,
The error you’re receiving is describing a problem with your analysis approach: if your project contains C#/.NET code, then the SonarScanner for .NET and not the plain sonar-scanner must be used for analysis.
We don’t currently have an easy/explicit tooling support for analyzing .NET code on GitLab; you can refer to this earlier thread for pointers. Basically you’re going to have to either use the dotnet CLI or a Windows-based image for running this particular pipeline.