[fix][PALF] migrating/replicating replicas as learners

Co-authored-by: oceanoverflow <oceanoverflow@gmail.com>
Co-authored-by: joseph12138 <17862707376@163.com>

src/share/ob_debug_sync_point.h

@@ -543,6 +543,7 @@ class ObString;
     ACT(STOP_TRANSFER_LS_LOGICAL_TABLE_REPLACED,)\
     ACT(BEFORE_TRANSFER_DOING,)\
     ACT(BEFORE_BUILD_LS_MIGRATION_DAG_NET,)\
+    ACT(AFTER_JOIN_LEARNER_LIST,)\
     ACT(MAX_DEBUG_SYNC_POINT,)
 
 DECLARE_ENUM(ObDebugSyncPoint, debug_sync_point, OB_DEBUG_SYNC_POINT_DEF);