feat: fix CI failure: replace deprecated cedx/setup-dart with dart-lang/setup-dart

[Copilot]

The publish job fails with "Unable to resolve action cedx/setup-dart, repository not found" because the third-party action is deprecated/removed.

Changes

• Replace cedx/setup-dart@v2 with official dart-lang/setup-dart@v1 in publish job
• Add sdk: stable parameter to match analyze/test jobs

# Before
- uses: cedx/setup-dart@v2

# After  
- uses: dart-lang/setup-dart@v1
  with:
    sdk: stable

This aligns all three jobs (analyze, test, publish) to use the same maintained Dart setup action.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>[bug] fix CI error</issue_title>
<issue_description>See: https://github.com/casbin/dart-casbin/actions/runs/19468089921/job/55707928820

[publish](https://github.com/casbin/dart-casbin/actions/runs/19468089921/job/55707928820#logs)
failed 37 minutes ago in 3s
Search logs
1s
Current runner version: '2.329.0'
Runner Image Provisioner
Operating System
Runner Image
GITHUB_TOKEN Permissions
Secret source: Actions
Prepare workflow directory
Prepare all required actions
Getting action download info
Error: Unable to resolve action cedx/setup-dart, repository not found
```</issue_description>

## Comments on the Issue (you are @copilot in this section)

<comments>
</comments>

• Fixes [bug] fix CI error #64

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