CI: Add Dependabot config for maintaining GH actions

[danielhollas]

Last PR related to CI (promise!), I saved the perhaps controversial change for last. :-)

Added a dependabot config for maintaining GH actions (NOT Python dependencies). It updates monthly, and should be even less frequent since we typically don't pin to the exact versions of the Actions, and major version updates are infrequent.

Also tried to simplify a bit the release workflow by utilizing the newly added pytest -m presto tests.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 77.73%. Comparing base (ef60b66) to head (84ec7f9). Report is 40 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #6467 +/- ## ========================================== + Coverage 77.51% 77.73% +0.23% ========================================== Files 560 561 +1 Lines 41444 41724 +280 ========================================== + Hits 32120 32432 +312 + Misses 9324 9292 -32 ```

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