Merge pull request #4501 from Sergio0694/fix/remove-net-core-2.1

Bump Notifications test project to .NET Core 3.1

Author: michael-hawker

UnitTests/UnitTests.Notifications.NetCore/UnitTests.Notifications.NetCore.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netcoreapp2.1</TargetFrameworks>
+    <TargetFrameworks>netcoreapp3.1</TargetFrameworks>
   </PropertyGroup>
 
   <ItemGroup>