Fix CI for upload artifact breaking change

[amstilp]

• pin all actions to their latest version, so updates can be handled by dependabot
• fix coverage steps so that it works with the latest version of github actions' upload-artifact (which includes a breaking change to not upload hidden files)

[codecov[bot]]

Codecov Report

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

Project coverage is 99.01%. Comparing base (2feaa88) to head (18a236f). Report is 5 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #729 +/- ## ======================================= Coverage 99.01% 99.01% ======================================= Files 325 325 Lines 30708 30708 ======================================= Hits 30406 30406 Misses 302 302 ```

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