Fix GitHub Actions

Author: bahusoid

.github/workflows/NetCoreTests.yml

@@ -48,9 +48,11 @@ jobs:
 
     - uses: actions/checkout@v2
     - name: Setup .NET
-      uses: actions/setup-dotnet@v1.8.0
+      uses: actions/setup-dotnet@v1
       with:
-        dotnet-version: 2.1.x
+      dotnet-version: |
+        2.1.x
+        3.1.x
 
     - name: Build and Test
       run: |