Upgrade .Net version in asp.net-webservice sample

[Adam-it]

❓ Why

The .Net sample is Net 6 which end of support was November 12, 2024.
I think it would be nice to refresh the sample and update the sample to any of the supported .Net versions either:

• LTS - Net 8 with end of support till November 10, 2026 (recommended IMO)
• STS - Net 9 with endo of support till May 12, 2026

🎯 Aim

The aim is to update the Net version in Demo.csproj and update the NuGets packages to higher version that could correspond to Net version.

🙋‍♂️

If possible I may rise a PR with this change.