xunit.v3 support

[adam-knights]

XUnit.v3 is now available: https://xunit.net/releases/v3/1.0.0

Discussion for supporting that.

It's a package rename, so we may prefer Reqnroll.xUnit.v3 too?

[kaylumah]

One example I have found online is keeping both versions of the package alive, like for example done by Verify
https://github.com/VerifyTests/Verify

https://www.nuget.org/packages/Verify.XunitV3/
https://www.nuget.org/packages/Verify.Xunit/

Doing the same would not force people to migrate if they don't which to migrate.

[kaylumah]

Due note, we also have this plugin (and perhaps others) https://github.com/reqnroll/Reqnroll/blob/main/Plugins/Reqnroll.Verify/Reqnroll.Verify.ReqnrollPlugin/Reqnroll.Verify.ReqnrollPlugin.csproj

That explicitly use the old version of xunit

[ajeckmans]

Yes and we definitely need a v3 version of that since verify has one as well