add hybrid_fsdp_expt_group in pg_collection

Author: Jinliang Li

megatron/core/distributed/fsdp/mcore_fsdp_adapter.py

@@ -236,6 +236,7 @@ def _init_dist_index(self, pg_collection):
                 hybrid_fsdp_group = pg_collection.dp_cp
                 # This has not been tested yet.
                 expt_dp_group = getattr(pg_collection, 'intra_expt_dp', None)
+                hybrid_fsdp_expt_group = getattr(pg_collection, 'expt_dp', None)
                 ep_group = getattr(pg_collection, 'ep', None)
             else:
                 dp_cp_group = pg_collection.dp_cp