[Cherry-Pick][CI] Pin gunicorn version to 25.0.3(#6497)

[EmmonsCurse]

Cherry-pick of #6497 (authored by @EmmonsCurse) to release/2.4.

devPR:#6497

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Motivation

Recent CI runs were affected by unexpected behavior caused by automatic upgrades of gunicorn. Without an explicit version constraint, the runtime environment became inconsistent, leading to instability across different executions.

To ensure reproducibility and avoid potential compatibility issues, the gunicorn version needs to be pinned explicitly.

Modifications

• Pin gunicorn version to 25.0.3
• Prevent unintended upgrades from dependency resolution or base image updates
• Improve CI environment stability and consistency

Usage or Command

N/A

Accuracy Tests

N/A

Checklist

• Add at least a tag in the PR title.
• Tag list: [[FDConfig],[APIServer],[Engine], [Scheduler], [PD Disaggregation], [Executor], [Graph Optimization], [Speculative Decoding], [RL], [Models], [Quantization], [Loader], [OP], [KVCache], [DataProcessor], [BugFix], [Docs], [CI], [Optimization], [Feature], [Benchmark], [Others], [XPU], [HPU], [GCU], [DCU], [Iluvatar], [Metax]]
• You can add new tags based on the PR content, but the semantics must be clear.
• Format your code, run pre-commit before commit.
• Add unit tests. Please write the reason in this PR if no unit tests.
• 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

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (release/2.4@2b79d97). Learn more about missing BASE report.

Additional details and impacted files

@@              Coverage Diff               @@
##             release/2.4    #6543   +/-   ##
==============================================
  Coverage               ?   56.32%           
==============================================
  Files                  ?      333           
  Lines                  ?    42351           
  Branches               ?     6443           
==============================================
  Hits                   ?    23855           
  Misses                 ?    16630           
  Partials               ?     1866           

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