Fix ckpt done

[gongel]

PR types

• Bug fixes

PR changes

• APIs

Description

• checkpoint_done原先会被存两次，AFS不支持追加写，导致失败。现将ckpt和最后保存的模型分开标识。

[paddle-bot]

Thanks for your contribution!

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 55.42%. Comparing base (6b3875c) to head (cc8ab87).
Report is 6 commits behind head on develop.

Files	Patch %	Lines
paddlenlp/trainer/trainer.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #8402   +/-   ##
========================================
  Coverage    55.42%   55.42%           
========================================
  Files          615      615           
  Lines        96235    96235           
========================================
  Hits         53335    53335           
  Misses       42900    42900           

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