ci: 🎡 upgrade github actions to v4

[chimurai]

• run on ubuntu-latest
• upgrade github actions to v4

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/ngneat/spectator/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[x] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

Deprecation warning messages in github action builds:

⚠️ Node.js 16 actions are deprecated. Please update the following actions to use Node.js 20: actions/checkout@v2, actions/cache@v2.

• https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20
• https://github.blog/changelog/2024-04-16-deprecation-notice-v3-of-the-artifact-actions/

Build with warnings: https://github.com/ngneat/spectator/actions/runs/9570842990

What is the new behavior?

✅ build with no warnings

https://github.com/chimurai/spectator/actions/runs/9572409980

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

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