solve race in replication test due to ping (#11609)

attach_to_replication_stream already stops pings, but it stops them on
the server we connect to, and in this case it's a replica, and we need
to stop them on the real master.

tests/integration/replication.tcl

@@ -226,6 +226,9 @@ start_server {tags {"repl external:skip"}} {
         }
 
         test {FLUSHDB / FLUSHALL should replicate} {
+            # we're attaching to a sub-replica, so we need to stop pings on the real master
+            r -1 config set repl-ping-replica-period 3600
+
             set repl [attach_to_replication_stream]
 
             r -1 set key value