Go back to using nuget.exe for restore

Author: christophwille

.github/workflows/dotnet.yml

@@ -29,7 +29,9 @@ jobs:
       uses: actions/setup-dotnet@v1
       with:
         dotnet-version: 5.0.x
-    - run: dotnet restore WpfDesign.sln
+    - name: Setup NuGet.exe
+      uses: nuget/setup-nuget@v1
+    - run: nuget restore WpfDesign.sln
     - name: Build
       run: dotnet build WpfDesign.sln --no-restore -c ${{ matrix.configuration }}
     - name: Test