MDEV-32651: Lost Debug_sync signal in rpl_sql_thd_start_errno_cleared

The test rpl.rpl_sql_thd_start_errno_cleared can lose a debug_sync
signal, as there is a RESET immediately following a SIGNAL. When the
signal is lost, the sql_thread is stuck in a WAIT_FOR clause until
it times out, resulting in long test times (albeit still
successful).

This patch extends the test to ensure the debug_sync signal was
received before issuing the RESET

mysql-test/suite/rpl/r/rpl_sql_thd_start_errno_cleared.result

@@ -34,6 +34,7 @@ set debug_sync= "now wait_for sql_thread_run_lock_released";
 # Validating that Last_SQL_Errno is cleared..
 # ..success
 set debug_sync= "now signal sql_thread_continue";
+# Wait for debug_sync signal to have been received before issuing RESET
 set @@global.debug_dbug= @saved_dbug;
 set debug_sync= "RESET";
 # Cleanup

mysql-test/suite/rpl/t/rpl_sql_thd_start_errno_cleared.test

@@ -76,6 +76,10 @@ if ($last_error)
 
 set debug_sync= "now signal sql_thread_continue";
 
+--echo # Wait for debug_sync signal to have been received before issuing RESET
+let $wait_condition= select count(*)=0 from information_schema.processlist where state like "debug sync point%";
+source include/wait_condition.inc;
+
 set @@global.debug_dbug= @saved_dbug;
 set debug_sync= "RESET";