Initialize SecurityRequirements

React to breaking change in microsoft/OpenAPI.NET#1797.

Author: martincostello

src/TodoApp/OpenApi/AspNetCore/AspNetCoreOpenApiEndpoints.cs

@@ -49,6 +49,7 @@ public static IServiceCollection AddAspNetCoreOpenApi(this IServiceCollection se
                 document.Components ??= new();
                 document.Components.SecuritySchemes ??= new Dictionary<string, OpenApiSecurityScheme>();
                 document.Components.SecuritySchemes[scheme.Reference.Id] = scheme;
+                document.SecurityRequirements ??= [];
                 document.SecurityRequirements.Add(new() { [scheme] = [] });
 
                 return Task.CompletedTask;