Update dotnetcore.yml

.github/workflows/dotnetcore.yml

@@ -9,6 +9,12 @@ jobs:
     
     steps:
     - uses: actions/checkout@v2
+    - name: Setup dotnet 6.x
+      uses: actions/setup-dotnet@v1
+      with:
+          dotnet-version: '6.x'
+    - name: Display dotnet version
+      run: dotnet --version
           
     - name: setup-msbuild
       uses: microsoft/setup-msbuild@v1