Update sonar.yml

Author: danny-gallagher

.github/workflows/sonar.yml

@@ -25,7 +25,7 @@ jobs:
       - name: Setup .NET 6
         uses: actions/[email protected]
         with:
-          dotnet-version: 6.0.x
+          dotnet-version: 3.1
       - name: Setup java
         uses: actions/setup-java@v1
         with: