Add net6.0 target framework in console project

[taoyouh]

Description:

This PR add a net6.0 target to the console project. Users with only .NET 6 runtime installed can run the console tool after this change.

Fixes #378

Checklist:

• [x] I have commented my code, particularly in hard-to-understand areas
• [x] My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes
• [ ] I have tested my changes by running the extension in VS2017
• [ ] I have tested my changes by running the extension in VS2019
• [ ] I have tested my changes by running the extension in VS2022
• [ ] If changes to the documentation are needed, I have noted this in the description above

[grochocki]

Thanks for the contribution @taoyouh! This was just addressed in #379 and published in XamlStyler.Console 3.2206.4. Safe to close?

[taoyouh]

I'm thinking of having multi-target will provide better compatibility. If we keep the .NET Core 3.1 target, developers that are still using old SDK can still use this tool.