Fix CoreML P6 inference (ultralytics#6700)

* Fix CoreML P6 inference

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

models/common.py

@@ -428,7 +428,8 @@ def forward(self, im, augment=False, visualize=False, val=False):
                 conf, cls = y['confidence'].max(1), y['confidence'].argmax(1).astype(np.float)
                 y = np.concatenate((box, conf.reshape(-1, 1), cls.reshape(-1, 1)), 1)
             else:
-                y = y[sorted(y)[-1]]  # last output
+                k = 'var_' + str(sorted(int(k.replace('var_', '')) for k in y)[-1])  # output key
+                y = y[k]  # output
         else:  # TensorFlow (SavedModel, GraphDef, Lite, Edge TPU)
             im = im.permute(0, 2, 3, 1).cpu().numpy()  # torch BCHW to numpy BHWC shape(1,320,192,3)
             if self.saved_model:  # SavedModel