Install dotnet 6

Author: lyndon-gabriel

.github/workflows/test-net60.yaml

@@ -8,6 +8,11 @@ jobs:
         uses: actions/checkout@v2
         with:
           submodules: 'recursive'
+      - name: Setup dotnet
+        uses: actions/setup-dotnet@v4
+        with:
+          dotnet-version: |
+            6.0.x
       - name: Run the Core tests
         run: dotnet test $GITHUB_WORKSPACE/tests/Medidata.MAuth.CoreTests --framework net6.0
       - name: Run the ASP.NET Core tests