Update xunit to v3

Author: voytas

tests/Spectron.Files.Tests/Spectron.Files.Tests.csproj

@@ -14,7 +14,7 @@
     <ItemGroup>
         <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.0.1" />
         <PackageReference Include="Shouldly" Version="4.3.0" />
-        <PackageReference Include="xunit" Version="2.9.3" />
+        <PackageReference Include="xunit.v3" Version="3.2.2" />
         <PackageReference Include="xunit.runner.visualstudio" Version="3.1.5">
             <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
             <PrivateAssets>all</PrivateAssets>