Add dependabot and update CI a bit

[devmotion]

I noticed that quite a few of our Github actions in CI are outdated. The PR adds dependabot which will open PRs for updating them automatically. For it to be more useful, I changed a few actions that were set to latest to a proper version such as v1. Moreover, the PR updates the CompatHelper CI setup.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (9a2f7bb) 72.78% compared to head (982784c) 67.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #540      +/-   ##
==========================================
- Coverage   72.78%   67.00%   -5.78%     
==========================================
  Files          52       52              
  Lines        1374     1373       -1     
==========================================
- Hits         1000      920      -80     
- Misses        374      453      +79     

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