MDEV-26626 fixup: Do not advance checkpoint during startup

While the redo log is being resized in srv_start(),
we must not write checkpoint information to the old log.

Thanks to Matthias Leich for noticing this.

storage/innobase/buf/buf0flu.cc

@@ -2271,7 +2271,9 @@ static os_thread_ret_t DECLARE_THREAD(buf_flush_page_cleaner)(void*)
 
       mysql_mutex_unlock(&buf_pool.flush_list_mutex);
 
-      if (!recv_recovery_is_on() && srv_operation == SRV_OPERATION_NORMAL)
+      if (!recv_recovery_is_on() &&
+          !srv_startup_is_before_trx_rollback_phase &&
+          srv_operation == SRV_OPERATION_NORMAL)
         log_checkpoint();
 
       mysql_mutex_lock(&buf_pool.flush_list_mutex);