MDEV-35570 parallel slave ALTER-SEQUENCE attempted to binlog out-of-order

Since MDEV-31503 fixes ALTER-SEQUENCE might be able to  complete its
work including binlogging before a preceding in binlog-order
transaction. There may not be data dependency between the two
transactions, but there would be
   "an attempt was made to binlog GTID D-S-XYZ which would create an
   out-of-order sequence number"
error in the gtid_strict_mode = ON.

After the preceding transaction started committing, and does it rather
slow, ALTER-SEQUNCE was able to find a time window to complete because
it temporarily releases its link with the waitee parent transaction.
And while having it released it also erroneously executes the binlogging part.

Fixed with restoring the commit dependency on the parent before
ALTER-SEQUNCE takes on binlogging.

sql/rpl_parallel.cc

@@ -1537,6 +1537,14 @@ handle_rpl_parallel_thread(void *arg)
           else
             rgi->mark_start_commit();
           DEBUG_SYNC(thd, "rpl_parallel_after_mark_start_commit");
+#ifdef ENABLED_DEBUG_SYNC
+          DBUG_EXECUTE_IF("halt_past_mark_start_commit",
+          {
+            DBUG_ASSERT(!debug_sync_set_action
+                        (thd, STRING_WITH_LEN("now WAIT_FOR past_mark_continue")));
+            DBUG_SET_INITIAL("-d,halt_past_mark_start_commit");
+          };);
+#endif
         }
       }