Still install .NET 6 and 7 for samples

Author: ThomasArdal

.github/workflows/dotnet-core.yml

@@ -18,6 +18,8 @@ jobs:
       uses: actions/setup-dotnet@v4
       with:
         dotnet-version: |
+          6.0.x
+          7.0.x
           8.0.x
           9.0.x