Det models with `nc=1` when `single_cls=True` (#19381)

Signed-off-by: Kevin Serrano <35779409+kevinconka@users.noreply.github.com>

ultralytics/engine/trainer.py

@@ -567,6 +567,10 @@ class BaseTrainer:
         except Exception as e:
             raise RuntimeError(emojis(f"Dataset '{clean_url(self.args.data)}' error ❌ {e}")) from e
         self.data = data
+        if self.args.single_cls:
+            LOGGER.info("Overriding class names with single class.")
+            self.data["names"] = {0: "item"}
+            self.data["nc"] = 1
         return data["train"], data.get("val") or data.get("test")
 
     def setup_model(self):