Update dependency NSubstitute to v6

Author: renovate[bot]

Cake.Frosting.Issues.Recipe/Cake.Frosting.Issues.Recipe.Tests/Cake.Frosting.Issues.Recipe.Tests.csproj

@@ -26,7 +26,7 @@
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.7.0" />
-    <PackageReference Include="NSubstitute" Version="5.3.0" />
+    <PackageReference Include="NSubstitute" Version="6.2.0" />
     <PackageReference Include="xunit" Version="2.9.3" />
     <PackageReference Include="xunit.runner.visualstudio" Version="3.1.5">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets>