Workflow Adjustments

[Zeitsperre]

Changes

• Actions have been updated to more recent versions
• pip-based dpeendencies used to run on CI are now managed by a CI/requirements_ci.txt that uses hashes of packages for security
• Warnings in Pull Requests from forks are now less buggy
• The yamllint configuration is a bit stricter but is now consistent for all YAML files in the repository, including the GitHub Workflows
• Documentation has been added for make initialize-translations
• A new pre-commit hook for validating numpy doctsrings has been added (using numpydoc).
• Dependencies have been updated and synchronized
• The top-level repository workflow is now using security hardening and hashed commits where possible

[aulemahal]

Looks good to me!