Update dotnet.yml (#42)

Author: BorisDog

.github/workflows/dotnet.yml

@@ -14,6 +14,11 @@ jobs:
     steps:
     - uses: actions/checkout@v3
 
+    - name: Setup dotnet
+      uses: actions/setup-dotnet@v3
+      with:
+          dotnet-version: 3.1.x
+      
     - name: Setup msbuild
       uses: microsoft/[email protected]