Update dependency NUnit to v5

Author: renovate[bot]

tests/Markdown.ColorCode.UnitTests/Markdown.ColorCode.UnitTests.csproj

@@ -29,7 +29,7 @@
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>
-    <PackageReference Include="NUnit" Version="4.6.1" />
+    <PackageReference Include="NUnit" Version="5.0.0" />
     <PackageReference Include="NUnit3TestAdapter" Version="6.3.0" />
     <PackageReference Include="StyleCop.Analyzers" Version="1.1.118">
       <PrivateAssets>all</PrivateAssets>