Bump NUnit from 3.7.1 to 3.13.2

Bumps [NUnit](https://github.com/nunit/nunit) from 3.7.1 to 3.13.2.
- [Release notes](https://github.com/nunit/nunit/releases)
- [Changelog](https://github.com/nunit/nunit/blob/v3.13.2/CHANGES.md)
- [Commits](nunit/nunit@3.7.1...v3.13.2)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

src/core/Akka.Streams.Tests.TCK/Akka.Streams.Tests.TCK.csproj

@@ -25,7 +25,7 @@
     <!-- !!!WARNING!!! 
          NUNIT VERSION HAVE TO MATCH WITH THE VERSION USED BY REACTIVE TCK. 
          !!!WARNING!!! -->
-    <PackageReference Include="NUnit" Version="3.7.1" Condition="'$(TargetFramework)' == '$(NetCoreTestVersion)'"/>
+    <PackageReference Include="NUnit" Version="3.13.2" Condition="'$(TargetFramework)' == '$(NetCoreTestVersion)'"/>
   </ItemGroup>
 
   <PropertyGroup Condition=" '$(TargetFramework)' == '$(NetFrameworkTestVersion)' ">