fix pylayer forward memleak (#44826)

paddle/fluid/eager/pylayer/py_layer_node.h

@@ -31,6 +31,7 @@ class GradNodePyLayer : public GradNodeBase {
                   size_t bwd_out_slot_num)
       : GradNodeBase(bwd_in_slot_num, bwd_out_slot_num) {
     ctx_ = ctx;
+    Py_INCREF(ctx_);
   }
 
   ~GradNodePyLayer() override { Py_XDECREF(ctx_); };

paddle/fluid/pybind/eager_py_layer.cc

@@ -383,6 +383,7 @@ PyObject* pylayer_method_apply(PyObject* cls,
   Py_XDECREF(kwargs_value_list);
   Py_XDECREF(backward_function);
   Py_XDECREF(forward_fn);
+  Py_XDECREF(ctx);
 
   return outputs;
   EAGER_CATCH_AND_THROW_RETURN_NULL