Upgrade CI Node.js versions from 16 & 18 to 20 & 22

[Copilot]

Updates GitHub Actions workflows to use Node.js 20 and 22 instead of the EOL versions 16 and 18.

Changes

• Updated matrix strategy in .github/workflows/main.yml for both test and coverall jobs
• Node versions specified as strings per GitHub Actions conventions

matrix:
  node-version: ['20', '22']  # Previously [^16, ^18]

Original prompt

---

This section details on the original issue you should resolve

<issue_title>[feature] upgrade all CI scripts' Node.js version from 16 & 18 to 20 & 22</issue_title>
<issue_description></issue_description>

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

@hsluoyz @nodece @Shivansh-yadav13

• Fixes [feature] upgrade all CI scripts' Node.js version from 16 & 18 to 20 & 22 #84

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[hsluoyz]

@nodece @Shivansh-yadav13 please review

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