Update GitHub Actions and enable Dependabot

[8Keep]

Updating current github actions and enabling dependabot for github actions from now on.

[gemini-code-assist]

Code Review

This pull request updates the Dependabot configuration to include tracking for GitHub Actions. The new configuration specifies a weekly update schedule, a limit of five open pull requests, a 'ci' commit message prefix, and relevant labels for these dependency updates. I have no feedback to provide as no issues were identified and no review comments were present.

[riccardobl]

Thanks!
I took the liberty of making a few changes to this PR:

• downgraded some GitHub Actions that were released very recently to slightly older versions
• added a 30 days cooldown to Dependabot

The goal is to avoid tracking the very latest releases immediately, giving some time for potential supply-chain attacks to surface before we upgrade.

[8Keep]

Thanks @riccardobl, those changes sound good to me too. I don't think I can merge, let me know when you can do that.