fix: 修复解决拉取请求冲突时未更新主分支的问题

[BigOrangeQWQ]

No description provided.

[Copilot]

Pull Request Overview

This PR addresses an issue where the functionality responsible for resolving pull request conflicts was not correctly updating the local branch with the latest remote changes.

• Added a "git pull origin master" command in tests to simulate fetching the latest remote branch.
• Introduced a new update_branch method in the git handler and integrated it into the publish utility to update the branch before checkout.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
tests/plugins/github/resolve/test_resolve_pull_request.py	Added a git pull command to ensure tests fetch the latest remote branch.
src/plugins/github/plugins/publish/utils.py	Updated the branch before checkout by adding a call to handler.update_branch.
src/plugins/github/handlers/git.py	Added an update_branch method to execute a git pull for the specified branch.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.67%. Comparing base (c087c10) to head (cc9c594).
Report is 1 commits behind head on main.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #384   +/-   ##
=======================================
  Coverage   93.67%   93.67%           
=======================================
  Files          41       41           
  Lines        2276     2278    +2     
=======================================
+ Hits         2132     2134    +2     
  Misses        144      144           

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