Update Newtonsoft.Json from 12.0.2 to 12.0.3 in Compatibility project as well

[bergmeister]

PR Summary

PowerShell 6.2.4 uses this version as well, therefore not an issue: https://github.com/PowerShell/PowerShell/blob/v6.2.4/src/System.Management.Automation/System.Management.Automation.csproj
The upgrade to this version technically already happened in PR #1425 but this project was did not get updates.

PR Checklist

• PR has a meaningful title
  • Use the present tense and imperative mood when describing your changes
• Summarized changes
• Change is not breaking
• Make sure all .cs, .ps1 and .psm1 files have the correct copyright header
• Make sure you've added a new test if existing tests do not effectively test the code changed and/or updated documentation
• This PR is ready to merge and is not Work in Progress.
  • If the PR is work in progress, please add the prefix WIP: to the beginning of the title and remove the prefix when the PR is ready.

[bergmeister]

That's funny, one of the tests jobs failed because I merged PR #1446 AFTER the build had already started, meaning that when the test job checked out out the repo, it executed the newly added tests but of course the build artefact did not have the code to make it pass that test... I suppose this does not happen very often but it's good to be aware of this because the traditional re-run of the test stage did not help here of course. Technically, we should probably upload the Tests folder as an artefact to avoid this but that would make CI unnecessarily more complex I fear.