Update GitHub Actions to Latest Node Version

[mhellmeier]

🚀 Feature Request

Current Problem

The following information is displayed in the GitHub actions, like the build of the GitHub page for the documentation:

Node.js 16 actions are deprecated. Please update the following actions to use Node.js 20: gradle/gradle-build-action@v2. For more information see: https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/.

See: https://github.com/FraunhoferISST/TREND/actions/runs/9204230070

Proposed Solution

Update the workflows so that the latest versions are used.

Additional Context

Note that there are changes in the gradle-build-action. See the README of their GitHub Repo for more information.