fix(SwaggerGen): include endpoints with unmatching GroupName in OpenAPI document

When an endpoint's GroupName does not match any registered document,
treat it as ungrouped and include it in all documents. This fixes the
issue where endpoints with WithGroupName() configured would not appear
in the OpenAPI document when no corresponding document was registered.

Before: GroupName set but not matching docName → endpoint excluded
After:  GroupName set but not matching any registered doc → included

Author: bobo-xxx

src/Swashbuckle.AspNetCore.SwaggerGen/SwaggerGenerator/SwaggerGeneratorOptions.cs

@@ -81,7 +81,10 @@ public SwaggerGeneratorOptions()
 
     private bool DefaultDocInclusionPredicate(string documentName, ApiDescription apiDescription)
     {
-        return apiDescription.GroupName == null || apiDescription.GroupName == documentName;
+        // If the endpoint's GroupName doesn't match any registered document, treat it as
+        // ungrouped (include it). This ensures endpoints with a GroupName that's not mapped
+        // to a specific document are not inadvertently excluded from the OpenAPI document.
+        return !_options.SwaggerDocs.ContainsKey(apiDescription.GroupName) || apiDescription.GroupName == documentName;
     }
 
     private string DefaultOperationIdSelector(ApiDescription apiDescription)