Stabilize dual replication test to avoid getting LOADING error (valkey-io#1979)

Supplement the repair of valkey-io#1288,
need to wait for the Loading to complete before executing
`$replica replicaof no one`.

Signed-off-by: artikell <739609084@qq.com>

Author: artikell

tests/integration/dual-channel-replication.tcl

@@ -773,6 +773,7 @@ start_server {tags {"dual-channel-replication external:skip"}} {
         set load_handle0 [start_write_load $primary_host $primary_port 60]
         set load_handle1 [start_write_load $primary_host $primary_port 60]
         set load_handle2 [start_write_load $primary_host $primary_port 60]
+        set replica_loglines [count_log_lines 0]
 
         $replica config set dual-channel-replication-enabled yes
         $replica config set loglevel debug
@@ -801,12 +802,14 @@ start_server {tags {"dual-channel-replication external:skip"}} {
             # In this way, in the subsequent replicaof no one, we won't get the LOADING error if the replica reconnects
             # too quickly and enters the loading state.
             $primary debug pause-after-fork 1
+            set replica_loglines [count_log_lines 0]
             resume_process $replica_pid
             set res [wait_for_log_messages -1 {"*Unable to partial resync with replica * for lack of backlog*"} $loglines 2000 10]
             set loglines [lindex $res 1]
         }
         # Waiting for the primary to enter the paused state, that is, make sure that bgsave is triggered.
         wait_process_paused -1
+        wait_for_log_messages 0 {"*Done loading RDB*"} $replica_loglines 1000 10
         $replica replicaof no one
         # Resume the primary and make sure the sync is dropped.
         resume_process [srv -1 pid]