[Cherry-Pick][BugFix] Fix ErrorInfo code type(#6951)

[EmmonsCurse]

Cherry-pick of #6951 (authored by @sunlei1024) to release/2.4.

devPR:#6951

---

Motivation

This PR fixes a type error caused by inconsistent data types in the ErrorInfo.code field. The field expects a string type, but an integer was previously provided, leading to type validation or runtime issues.

Modifications

• Updated one line of code to ensure correct type usage:

• Changed code=0 to code='0' in ErrorInfo.

• This ensures consistency with the expected schema and avoids type-related errors.

Usage or Command

manually trigger the related API / functionality to confirm no type error is raised.

Accuracy Tests

This change does not affect model outputs or accuracy.

Checklist

• Add at least a tag in the PR title. ([BugFix])
• Format your code, run pre-commit before commit.
• Add unit tests. (Not added since this is a trivial one-line fix)
• Provide accuracy results.
• If the current PR is submitting to the release branch, make sure the PR has been submitted to the develop branch, then cherry-pick it to the release branch with the [Cherry-Pick] PR tag.

[paddle-bot]

Thanks for your contribution!

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (release/2.4@02d8e1a). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
fastdeploy/entrypoints/openai/api_server.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff               @@
##             release/2.4    #6953   +/-   ##
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  Coverage               ?   56.80%           
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  Files                  ?      333           
  Lines                  ?    42505           
  Branches               ?     6473           
==============================================
  Hits                   ?    24144           
  Misses                 ?    16465           
  Partials               ?     1896           

Flag	Coverage Δ
GPU	56.80% <0.00%> (?)

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