[Instrumentation.AspNetCore] Missing PR link in CHANGELOG (open-telemetry#2577)

Author: Kielek

src/OpenTelemetry.Instrumentation.AspNetCore/CHANGELOG.md

@@ -6,6 +6,7 @@
   Configurable with the
   `AspNetCoreTraceInstrumentationOptions.EnableAspNetCoreSignalRSupport`
   option which defaults to `true`. Only applies to .NET 9.0 or greater.
+  ([#2539](https://github.com/open-telemetry/opentelemetry-dotnet-contrib/pull/2539))
 
 ## 1.11.0