TestWebSite should use the same (LTS) version of .NET as other projects and already available on the ADO images

[jonthysell]

Problem Description

TestWebSite requires the .NET 7.0 SDK and installs it as part of running in CI. RNW images and our dependency script both require .NET 6.0 only.

Option 1 (Preferable):

1. Retarget TestWebSite to .NET 6.0 LTS which is already available
2. Remove the .NET install during CI.

Option 2:

1. Retarget TestWebSite to .NET 8.0 LTS
2. Retarget ManagedCodeGen to .NET 8.0 LTS
3. Update the ADO image to include .NET 8.0 instead of .NET 6.0
4. Update the dependency script to require .NET 8.0
5. Remove the .NET install during CI.

Steps To Reproduce

See CI.

Expected Results

No response

CLI version

npx react-native -v

Environment

npx react-native info

Target Platform Version

None

Target Device(s)

No response

Visual Studio Version

None

Build Configuration

None

Snack, code example, screenshot, or link to a repository

No response

[jonthysell]

TestWebSite added in #12714

[JunielKatarn]

Used .NET 7 to be able to develop it in macOS (Visual Studio for Mac does not support .NET 8).

I'll explore re-targeting to .NET 6.