Pin .NET version to 5.0.x

Author: gsvgit

.github/workflows/build-on-pr.yml

@@ -38,6 +38,8 @@ jobs:
 
       - name: Setup .NET Core
         uses: actions/setup-dotnet@v1
+        with:
+          dotnet-version: '5.0.x'
 
       - name: Build
         run: |
@@ -46,7 +48,7 @@ jobs:
         env:
           # Work around https://github.com/actions/setup-dotnet/issues/29
           DOTNET_ROOT: ${{ runner.tool_cache }}/dncs/${{ matrix.dotnet }}/x64
-          CI: true
+          CI: true        
 
   linux-test-self-hosted:
     name: Linux Self-Hosted Test