Bump nunit from 3.13.0 to 3.13.1

Bumps [nunit](https://github.com/nunit/nunit) from 3.13.0 to 3.13.1.
- [Release notes](https://github.com/nunit/nunit/releases)
- [Changelog](https://github.com/nunit/nunit/blob/master/CHANGES.md)
- [Commits](nunit/nunit@v3.13...v3.13.1)

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

Author: dependabot-preview[bot]

CircularBuffer.Tests/CircularBuffer.Tests.csproj

@@ -7,7 +7,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="nunit" Version="3.13.0" />
+    <PackageReference Include="nunit" Version="3.13.1" />
     <PackageReference Include="NUnit3TestAdapter" Version="3.17.0" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.8.3" />
   </ItemGroup>