Add dependabot config for github actions

[RincewindsHat]

No description provided.

[julianbrost]

Interesting idea but I'm not entirely sure if this will help us. I mean we reference other actions using something like @v3, which means if compatible changes are done to the action, we'll receive them automatically. So feels like the resulting PRs are less "you should update this" but more "there's a new version that's probably incompatible, maybe you want to use it".

No description provided.

What exactly was your motivation for creating this PR?

[RincewindsHat]

In other projects we got deprecation warnings for the pipelines after some time.
The specific versions seem to be nailed to a specific node version which does not get updated within the version of the action. Therefore those actions will have to be updated eventually (if Github continues this practice) and IMHO it is better to get receive a PR for that beforehand instead of getting a deprecation notice unexpectedly.

[Al2Klimov]

I, in contrast, don't even want a reason for applying updates – GHA or not.