[Eager] fix set_value logic when input's dtype is different (#48519)

* [Eager] fix set_value logic when input's dtype is different

* value_tensor

* fix set_value logic when input's dtype is different

paddle/fluid/pybind/eager_method.cc

@@ -1227,7 +1227,6 @@ static PyObject* tensor_method__setitem_eager_tensor(TensorObject* self,
             Py_TYPE(value_obj)));
       }
     }
-
     {
       // Release gil and do tracing
       py::gil_scoped_release release;
@@ -1242,6 +1241,9 @@ static PyObject* tensor_method__setitem_eager_tensor(TensorObject* self,
             self->tensor.name(), self->tensor, amp_dtype, "set_value");
         value_tensor = egr::EagerAmpAutoCast(
             value_tensor.name(), value_tensor, amp_dtype, "set_value");
+        if (self->tensor.dtype() != value_tensor.dtype()) {
+          value_tensor = cast_ad_func(value_tensor, self->tensor.dtype());
+        }
       }
       self->tensor = set_value__dygraph_function(
           self->tensor, value_tensor, {}, {}, {}, attrs);