Update TryExcept(msg='...')` (#9261)

utils/metrics.py

@@ -186,7 +186,7 @@ class ConfusionMatrix:
         # fn = self.matrix.sum(0) - tp  # false negatives (missed detections)
         return tp[:-1], fp[:-1]  # remove background class
 
-    @TryExcept('WARNING: ConfusionMatrix plot failure')
+    @TryExcept('WARNING: ConfusionMatrix plot failure: ')
     def plot(self, normalize=True, save_dir='', names=()):
         import seaborn as sn