fix can not find eager attr, test=develop (#38071)

python/paddle/fluid/eager/eager_tensor_patch_methods.py

@@ -20,4 +20,5 @@ def monkey_patch_eagertensor():
         from paddle.tensor.to_string import eager_tensor_to_string
         return eager_tensor_to_string(self)
 
-    setattr(core.eager.EagerTensor, "__str__", __str__)
+    if hasattr(core, "eager"):
+        setattr(core.eager.EagerTensor, "__str__", __str__)