build(deps): Bump xunit from 2.9.0 to 2.9.1 in /tests/OrasProject.Oras.Tests (#142)

Author: dependabot[bot]

tests/OrasProject.Oras.Tests/OrasProject.Oras.Tests.csproj

@@ -15,7 +15,7 @@
     </PackageReference>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
     <PackageReference Include="Moq" Version="4.20.72" />
-    <PackageReference Include="xunit" Version="2.9.0" />
+    <PackageReference Include="xunit" Version="2.9.1" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.8.2">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>