Improve tests coverage and speed (#4340)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

ultralytics/models/rtdetr/model.py

@@ -16,7 +16,7 @@ class RTDETR(Model):
     """
 
     def __init__(self, model='rtdetr-l.pt') -> None:
-        if model and not model.split('.')[-1] in ('pt', 'yaml', 'yml'):
+        if model and model.split('.')[-1] not in ('pt', 'yaml', 'yml'):
             raise NotImplementedError('RT-DETR only supports creating from *.pt file or *.yaml file.')
         super().__init__(model=model, task='detect')