Update dependency NSubstitute to 5.1.0

Author: renovate[bot]

tests/CacheTower.Tests/CacheTower.Tests.csproj

@@ -16,7 +16,7 @@
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>
     <PackageReference Include="Microsoft.NETFramework.ReferenceAssemblies" PrivateAssets="All" Version="1.0.3" />
-    <PackageReference Include="NSubstitute" Version="5.0.0" />
+    <PackageReference Include="NSubstitute" Version="5.1.0" />
   </ItemGroup>
 
   <ItemGroup>