Upgrade dependency versions and fix failing tests

[kailash-b]

Description

• Upgrade version of Microsoft.IdentityModel.Protocols.OpenIdConnect to 8.12.1
• Upgrade version of System.Text.Encodings.Web to 8.0.0

For test cases :

• Upgrades versions of the following
  • Framework from .NET 6 to .NET 8
  • FluentAssertions to 8.5.0
  • Microsoft.AspNetCore.Mvc.Testing to 8.0.*
  • Microsoft.AspNetCore.Mvc.ViewFeatures to 2.3.0
  • Microsoft.NET.Test.Sdk to 16.9.4
  • Moq to 4.20.72
  • xunit to 2.9.3
  • xunit.runner.visualstudio to 2.4.3
  • coverlet.collector to 6.0.*

References

• SDK-5567

Testing

• Setup repository on local and run all test cases on local.

• This change adds test coverage for new/changed/fixed functionality

Checklist

• I have added documentation for new/changed functionality in this PR or in auth0.com/docs
• All active GitHub checks for tests, formatting, and security are passing
• The correct base branch is being used, if not main