Add test project for c# 13 (pre-release version)

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 97.61905% with 1 line in your changes missing coverage. Please review.

Project coverage is 97.45%. Comparing base (ff5c432) to head (0187fb3).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #3864 +/- ## ======================================= Coverage 97.45% 97.45% ======================================= Files 926 931 +5 Lines 110237 110279 +42 Branches 3315 3315 ======================================= + Hits 107433 107474 +41 - Misses 1837 1838 +1 Partials 967 967 ```

[bjornhellander]

@sharwell, I created this mostly to check if there were any regressions so far. None found. Some previous Roslyn problems were fixed and some tests which have syntax errors in them got slightly different behavior, but looks good so far. If you think it is too early to merge this now, I can update this now and then until the time is right.

I added LanguageVersionEx.CSharp13 the way I expect it will be defined eventually even though it was not in place yet.

What do you think?

[sharwell]

Also need to incorporate this to https://github.com/DotNetAnalyzers/StyleCopAnalyzers/blob/master/build/build-and-test.yml

[bjornhellander]

Added that one and test.yml to the solution so they are easier to remember :-)