Bump xunit from 2.5.0 to 2.5.3 in /SteamKit2

Bumps [xunit](https://github.com/xunit/xunit) from 2.5.0 to 2.5.3.
- [Commits](https://github.com/xunit/xunit/commits)

---
updated-dependencies:
- dependency-name: xunit
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

SteamKit2/Tests/Tests.csproj

@@ -12,7 +12,7 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.AspNet.WebApi.Client" Version="5.2.9" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.7.2" />
-    <PackageReference Include="xunit" Version="2.5.0" />
+    <PackageReference Include="xunit" Version="2.5.3" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.5.0">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>