Compatible .NETCore versions

[AndrewBarzu]

Tried using the action with a project that runs on .NET 5, but I keep getting

The framework 'Microsoft.NETCore.App', version '3.1.2' was not found.
  - The following frameworks were found:
      5.0.11 at [C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\shared\Microsoft.NETCore.App]

This is the link to the failed workflow: https://github.com/PC-Chair-Fight/project-backend/runs/4132660755?check_suite_focus=true