Updated integration testing framework to major release

This is a build-only dependency and won't impact any downstream consumers.

Author: JeremyCaney

OnTopic.AspNetCore.Mvc.IntegrationTests/OnTopic.AspNetCore.Mvc.IntegrationTests.csproj

@@ -16,7 +16,7 @@
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
     </PackageReference>
-    <PackageReference Include="Microsoft.AspNetCore.Mvc.Testing" Version="5.0.5" />
+    <PackageReference Include="Microsoft.AspNetCore.Mvc.Testing" Version="6.0.1" />
   </ItemGroup>
 
   <ItemGroup>