changed the imgsize on enginge/prediction to meet the grayscale for prediction

ultralytics/engine/predictor.py

@@ -236,7 +236,7 @@ class BasePredictor:
 
         # Warmup model
         if not self.done_warmup:
-            self.model.warmup(imgsz=(1 if self.model.pt or self.model.triton else self.dataset.bs, 3, *self.imgsz))
+            self.model.warmup(imgsz=(1 if self.model.pt or self.model.triton else self.dataset.bs, 1, *self.imgsz))
             self.done_warmup = True
 
         self.seen, self.windows, self.batch, profilers = 0, [], None, (ops.Profile(), ops.Profile(), ops.Profile())