[CI] Unified diff coverage upload logic

[EmmonsCurse]

Motivation

Update the Codecov upload configuration to improve diff coverage reporting in CI. Ensure the diff coverage file is uploaded correctly with disable_search enabled and simplify the configuration.

Modifications

Updated Upload diff coverage report step.

Usage or Command

No changes to user commands

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 (develop@43097a5). Learn more about missing BASE report.

Additional details and impacted files

@@            Coverage Diff             @@
##             develop    #5127   +/-   ##
==========================================
  Coverage           ?   57.59%           
==========================================
  Files              ?      316           
  Lines              ?    38216           
  Branches           ?     5710           
==========================================
  Hits               ?    22011           
  Misses             ?    14461           
  Partials           ?     1744           

Flag	Coverage Δ
diff	57.59% <ø> (?)

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