ci: Update all GitHub Actions to latest versions and enable Dependabot

[Mrtenz]

This updates all GitHub Actions to the latest versions, fixes breaking changes where applicable, and enables Dependabot for GitHub Actions.

---

Note

Updates CI to latest GitHub Actions, replaces local security scan with reusable workflow, and enables Dependabot for GitHub Actions.

• CI workflows (.github/workflows/*):
  • Bump actions: MetaMask/action-checkout-and-setup → v2, actions/checkout → v6, actions/upload-artifact → v6, actions/download-artifact → v7.
  • Adjust steps to use updated actions across build, lint, test, E2E, platform-compat, publish, and PR update jobs; minor job/name tweaks and secret wiring (e.g., Codecov, PR update token).
• Security scanning:
  • Replace local security-code-scanner.yml with reusable MetaMask/action-security-code-scanner/.github/workflows/security-scan.yml@v2 and add paths-ignored, permissions, and secrets.
• Dependabot:
  • Enable updates for github-actions with allowlist for MetaMask/* and actions/* in .github/dependabot.yml (in addition to existing npm).
• Release/Publish workflows:
  • Apply action version bumps and artifact step updates in publish-release.yml, publish-environment.yml, publish-github-pages.yml, and publish-preview.yml without changing build/publish logic.

^{Written by Cursor Bugbot for commit 53edfd1. This will update automatically on new commits. Configure here.}

[github-advanced-security]

This pull request sets up GitHub code scanning for this repository. Once the scans have completed and the checks have passed, the analysis results for this pull request branch will appear on this overview. Once you merge this pull request, the 'Security' tab will show more code scanning analysis results (for example, for the default branch). Depending on your configuration and choice of analysis tool, future pull requests will be annotated with code scanning analysis results. For more information about GitHub code scanning, check out the documentation.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.33%. Comparing base (b58a9d1) to head (53edfd1).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3782   +/-   ##
=======================================
  Coverage   98.33%   98.33%           
=======================================
  Files         420      420           
  Lines       12032    12032           
  Branches     1874     1874           
=======================================
  Hits        11832    11832           
  Misses        200      200           

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🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
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[FrederikBolding]

I guess this matches test-utils