Use NET 5.0 in pipelines

Former-commit-id: f6e4e31c0a

.github/workflows/ci.yml

@@ -20,6 +20,6 @@ jobs:
     - name: Setup .NET Core
       uses: actions/setup-dotnet@v1
       with:
-        dotnet-version: 3.1.101
+        dotnet-version: 5.0
     - name: Test with dotnet
       run: dotnet test --logger GitHubActions

.github/workflows/release.yml

@@ -11,7 +11,7 @@ jobs:
     - name: Setup .NET Core
       uses: actions/setup-dotnet@v1
       with:
-        dotnet-version: 3.1
+        dotnet-version: 5.0
     - name: Build solution
       run: dotnet build --output build
     - name: Publish NuGet package