Moving WebJobs.Script to .NET 8

[fabiocav]

Issue describing the changes in this PR

This change updates the target for the WebJobs.Script project to .NET 8, enabling us to take advantage of some of the APIs and newer .NET features we need. The .NET standard target is no longer relevant for this project and maintaining this has become a hinderance.

Pull request checklist

IMPORTANT: Currently, changes must be backported to the in-proc branch to be included in Core Tools and non-Flex deployments.

• Backporting to the in-proc branch is not required
  • Otherwise: Link to backporting PR
• My changes do not require documentation changes
  • Otherwise: Documentation issue linked to PR
• 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
• My changes do not require diagnostic events changes
  • Otherwise: I have added/updated all related diagnostic events and their documentation (Documentation issue linked to PR)
• I have added all required tests (Unit tests, E2E tests)

Copilot reviewed 1 out of 2 changed files in this pull request and generated no comments.

Files not reviewed (1)

• src/WebJobs.Script/WebJobs.Script.csproj: Language not supported