Fixing build warning NETSSDK1138 when building projects with end-of-life .NET frameworks

In this short post I describe how to get rid of the following build warning: C:\Program Files\dotnet\sdk\5.0.100\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.EolTargetFrameworks.targets(28,5): warning NETSDK1138: The target framework 'netcoreapp2.0' is out of support and will not receive security updates in the future. Please refer to https://aka.ms/dotnet-core-support for more information about the support policy.