Enhancement: Run vimeo/psalm on GitHub Actions

[localheinz]

This pull request

• runs a static code analysis with vimeo/psalm on GitHub Actions

Follows #559.

[kamil-tekiela]

Given that we have very little test coverage (and are currently unable to name it), using a tool to run a static code analysis can improve our confidence in the changes we make.

That would help, but not by much. For me the biggest problem in this project is the interdependency with other repos and who knows what else. It's a jungle. There are scripts that call other scripts, execute functions, include files and more. This makes it difficult to refactor anything, because we don't know what has an impact on what.

[github-actions]

🚀 Commit db5ec41 Deployed on https://web-php-pr-892.preview.thephp.foundation

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

❗ No coverage uploaded for pull request base (master@42e335e). Click here to learn what that means.

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Additional details and impacted files

@@           Coverage Diff            @@
##             master    #892   +/-   ##
========================================
  Coverage          ?   0.14%           
  Complexity        ?      45           
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  Files             ?      49           
  Lines             ?   43151           
  Branches          ?       0           
========================================
  Hits              ?      64           
  Misses            ?   43087           
  Partials          ?       0           

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