fix recompute no grad warning (#38293)

Author: GuoxiaWang

python/paddle/distributed/fleet/utils/recompute.py

@@ -63,7 +63,8 @@ def swith_rng_state(rng_state):
 class RecomputeFunction(PyLayer):
  @staticmethod
  def forward(ctx, run_function, preserve_rng_state, *args):
- check_recompute_necessary(args)
+ if framework._dygraph_tracer()._has_grad:
+ check_recompute_necessary(args)
 
  # store for recomputing 
  ctx.run_function = run_function