forget to upgrade the time after the load stats timeout

[hawkingrei]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

after task timeout, we should upgrade the timeout checkpoint.

if we retry it immediately, it will timeout as soon as possible.

2. What did you expect to see? (Required)

3. What did you see instead (Required)

4. What is your TiDB version? (Required)