fix: benchmark workflow cannot post comment to PR

[greenhandatsjtu]

Fix: #294
I found benchmark workflow doesn’t work well that it fails to post comment to PR.
The reason is GITHUB_TOKEN only has read permission to pull requests when access by forked repos, so when a new PR is coming, running workflows only has read-only permission (of course not allowed to post comment). ref: https://docs.github.com/en/actions/security-guides/automatic-token-authentication#permissions-for-the-github_token

Luckily, GitHub has introduced a new event type: pull_request_target, which allows to run workflows from base branch and pass a token with write permission, so we can use it to post benchmark results to PR (ref: https://github.community/t/github-actions-are-severely-limited-on-prs/18179/17).

I modify pull_request.yml to use pull_request_target, now it works well:

[casbin-bot]

@smrpn @hackerchai @PsiACE @GopherJ please review

[codecov]

Codecov Report

Merging #298 (1ccd8bd) into master (663e764) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #298   +/-   ##
=======================================
  Coverage   81.46%   81.46%           
=======================================
  Files          23       23           
  Lines        3463     3463           
=======================================
  Hits         2821     2821           
  Misses        642      642           

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