Fix TOC: #65650 content lives inside OpenAPI section, not a new one

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Copilot

release-notes/11.0/preview/preview5/aspnetcore.md

@@ -11,7 +11,6 @@
 - [Blazor WebAssembly templates use Gateway](#blazor-webassembly-templates-use-gateway)
 - [Kestrel applies trailer header timeouts](#kestrel-applies-trailer-header-timeouts)
 - [OpenAPI schemas better match ASP.NET Core behavior](#openapi-schemas-better-match-aspnet-core-behavior)
-- [MVC and minimal APIs preserve multiple response types per status code](#mvc-and-minimal-apis-preserve-multiple-response-types-per-status-code)
 - [Bug fixes](#bug-fixes)
 - [Community contributors](#community-contributors)