Bump xunit from 2.5.0 to 2.8.0 in /src (#156)

Bumps [xunit](https://github.com/xunit/xunit) from 2.5.0 to 2.8.0.
- [Commits](xunit/xunit@2.5.0...2.8.0)

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

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

src/BBT.StructureTools.Tests/BBT.StructureTools.Tests.csproj

@@ -28,7 +28,7 @@
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.7.0" />
     <PackageReference Include="Moq" Version="4.20.69" />
     <PackageReference Include="Ninject" Version="3.3.6" />
-    <PackageReference Include="xunit" Version="2.5.0" />
+    <PackageReference Include="xunit" Version="2.8.0" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.5.0">
       <PrivateAssets>all</PrivateAssets>
     </PackageReference>