ProducesProblem not for route groups in .NET 8 (#33433)

* ProducesProblem not for route groups

* note methods that can't be used with route groups until .NET 9

* delete extraneous code fence tag

Author: tdykstra

aspnetcore/fundamentals/openapi/aspnetcore-openapi.md

@@ -304,7 +304,7 @@ app.MapGet("/todos", async (TodoDb db) =>
 
 #### Set responses for `ProblemDetails`
 
-When setting the response type for endpoints that may return a ProblemDetails response, the <xref:Microsoft.AspNetCore.Http.OpenApiRouteHandlerBuilderExtensions.ProducesProblem%2A> extension method or <xref:Microsoft.AspNetCore.Http.TypedResults.Problem%2A?displayProperty=nameWithType> can be used to add the appropriate annotation to the endpoint's metadata.
+When setting the response type for endpoints that may return a ProblemDetails response, the <xref:Microsoft.AspNetCore.Http.OpenApiRouteHandlerBuilderExtensions.ProducesProblem%2A> or <xref:Microsoft.AspNetCore.Http.OpenApiRouteHandlerBuilderExtensions.ProducesValidationProblem%2A> extension method or <xref:Microsoft.AspNetCore.Http.TypedResults.Problem%2A?displayProperty=nameWithType> can be used to add the appropriate annotation to the endpoint's metadata.
 
 When there are no explicit annotations provided by one of these strategies, the framework attempts to determine a default response type by examining the signature of the response. This default response is populated under the `200` status code in the OpenAPI definition.
 

aspnetcore/fundamentals/openapi/includes/aspnetcore-openapi6-8.md

@@ -133,7 +133,7 @@ app.MapGet("/todos", async (TodoDb db) =>
 
 ### Set responses for `ProblemDetails`
 
-When setting the response type for endpoints that may return a ProblemDetails response, the [`ProducesProblem`](/dotnet/api/microsoft.aspnetcore.http.openapiroutehandlerbuilderextensions.producesproblem) extension method or [`TypedResults.Problem`](/dotnet/api/microsoft.aspnetcore.http.typedresults.problem?) can be used to add the appropriate annotation to the endpoint's metadata.
+When setting the response type for endpoints that may return a ProblemDetails response, the <xref:Microsoft.AspNetCore.Http.OpenApiRouteHandlerBuilderExtensions.ProducesProblem%2A> extension method, <xref:Microsoft.AspNetCore.Http.OpenApiRouteHandlerBuilderExtensions.ProducesValidationProblem%2A>, or [`TypedResults.Problem`](/dotnet/api/microsoft.aspnetcore.http.typedresults.problem?) can be used to add the appropriate annotation to the endpoint's metadata. Note that the `ProducesProblem` and `ProducesValidationProblem` extension methods can't be used with [route groups](xref:fundamentals/minimal-apis/route-handlers#route-groups) in .NET 8 and earlier.
 
 When there are no explicit annotations provided by one of the strategies above, the framework attempts to determine a default response type by examining the signature of the response. This default response is populated under the `200` status code in the OpenAPI definition.