downgraded setup-dotnet step to v3

Author: Petr Sramek

.github/workflows/dotnet.yml

@@ -66,7 +66,7 @@ jobs:
     steps:
     - uses: actions/checkout@v3
     - name: Install .NET SDK
-      uses: actions/setup-dotnet@v4
+      uses: actions/setup-dotnet@v3
       with:
         dotnet-version: |
           2.0.x