Update Test Project to Target .NET 6 for WebJobs.Extensions.DurableTask Compatibility

[nytian]

Issue describing the changes in this PR

Changed several test project .csproj files to target .NET 6 since the latest versions of WebJobs.Extensions.DurableTask will only support .NET 6. This update is needed to restore packages correctly when running the publish CI.

Pull request checklist

• My changes do not require documentation changes
  • Otherwise: Documentation PR is ready to merge and referenced in pending_docs.md
• My changes should not be added to the release notes for the next release
  • Otherwise: I've added my notes to release_notes.md
• My changes do not need to be backported to a previous version
  • Otherwise: Backport tracked by issue/PR #issue_or_pr
• I have added all required tests (Unit tests, E2E tests)
• My changes do not require any extra work to be leveraged by OutOfProc SDKs
  • Otherwise: That work is being tracked here: #issue_or_pr_in_each_sdk
• My changes do not change the version of the WebJobs.Extensions.DurableTask package
  • Otherwise: major or minor version updates are reflected in /src/Worker.Extensions.DurableTask/AssemblyInfo.cs
• My changes do not add EventIds to our EventSource logs
  • Otherwise: Ensure the EventIds are within the supported range in our existing Windows infrastructure. You may validate this with a deployed app's telemetry. You may also extend the range by completing a PR such as this one.
• My changes should be added to v3.x branch.
  • Otherwise: This change only applies to Durable Functions v2.x and will not be merged to branch v3.x.

[cgillum]

LGTM. If there are any other projects that target netcoreapp3.1, we should probably update those as well so that we don't have any more of the older dependency.

[nytian]

Thanks for review! Just checking: should I also update this project? and the below one src/WebJobs.Extensions.DurableTask.Analyzers/WebJobs.Extensions.DurableTask.Analyzers.csproj @cgillum

[cgillum]

Things that are netstandard2.0 should be left as-is because there may be other compatibilities requirements that they have. But anything that's netcoreapp3.1 should be upgrade to net6.0.