feat: fix duplicate CI workflow runs on pull requests

[Copilot]

GitHub Actions workflows were running twice on PRs: once for the push event to the PR branch and once for the pull_request event, causing duplicate checks like "CI / macOS Latest (push)" and "CI / macOS Latest (pull_request)".

Changes

Updated workflow triggers in 4 files to run on push only for the master branch:

• .github/workflows/ci.yml
• .github/workflows/python_binding.yml
• .github/workflows/memcheck.yml
• .github/workflows/benchmark.yml

Before:

on: [push, pull_request]

After:

on:
  push:
    branches:
      - master
  pull_request:

PRs now trigger workflows once via pull_request event. Direct pushes to master still trigger via push event.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>[bug] needs to fix CI for strange duplicated checks in PR</issue_title>
<issue_description>The following duplicated CI checks ran in this open PR: #258

[CI / macOS Latest (pull_request)](https://github.com/casbin/casbin-cpp/actions/runs/19098521569/job/54571609532?pr=258)
CI / macOS Latest (pull_request)Failing after 21s
[CI / macOS Latest (push)](https://github.com/casbin/casbin-cpp/actions/runs/19098520831/job/54571609184?pr=258)
CI / macOS Latest (push)Failing after 18s
[Python Bindings Test / build (macos-latest, 3.8) (pull_request)](https://github.com/casbin/casbin-cpp/actions/runs/19098521581/job/54571609060?pr=258)
Python Bindings Test / build (macos-latest, 3.8) (pull_request)Failing after 1m
[Python Bindings Test / build (macos-latest, 3.8) (push)](https://github.com/casbin/casbin-cpp/actions/runs/19098520807/job/54571608791?pr=258)
Python Bindings Test / build (macos-latest, 3.8) (push)Failing after 1m
[Python Bindings Test / build (macos-latest, 3.10) (pull_request)](https://github.com/casbin/casbin-cpp/actions/runs/19098521581/job/54571609067?pr=258)
Python Bindings Test / build (macos-latest, 3.10) (pull_request)Failing after 50s
[Python Bindings Test / build (macos-latest, 3.10) (push)](https://github.com/casbin/casbin-cpp/actions/runs/19098520807/job/54571608773?pr=258)
Python Bindings Test / build (macos-latest, 3.10) (push)Failing after 37s

I think for an open state PR, it should not run "XXX (push)" checks, right? It should run for the git push after PR merge?
Need to fix the CI.</issue_description>

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

• Fixes [bug] needs to fix CI for strange duplicated checks in PR #259

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[github-actions]

🎉 This PR is included in version 1.63.0 🎉

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