Fix .NET version

Author: aalmada

.github/workflows/dotnetcore.yml

@@ -12,7 +12,8 @@ jobs:
     - name: Setup .NET Core
       uses: actions/setup-dotnet@v1
       with:
-        dotnet-version: 6.0.x
+        dotnet-version: '6.0.x'
+        include-prerelease: true
     - name: Test source generator
       run: dotnet test ./NetFabric.Hyperlinq.SourceGenerator.UnitTests/NetFabric.Hyperlinq.SourceGenerator.UnitTests.csproj 
     - name: Build solution