bump(actions): use actions that use n20

[DerTiedemann]

fixes #174 No of the listed actions had breaking changes according to the release notes:

• https://github.com/softprops/action-gh-release/releases/tag/v2.0.0
• https://github.com/ad-m/github-push-action/releases/tag/v0.8.0
• https://github.com/actions/checkout/releases/tag/v4.1.4