Validate Github Workflows/Actions

[Nicoretti]

Summary

Add nox task and an extra step to the CI workflow to ensure that the GitHub workflows/actions are valid.

Details

The most basic validation could involve checking the validity of the YAML files, for example by using appropriate linting tools.

Background & Context

Debugging and finding errors in actions and workflows can be tedious, as they usually only surface after being pushed or executed. Adding some way to validate them locally and in the CI pipeline would be beneficial.

Proposed Solution

1. Integrate a linting tool for validating YAML files in the CI pipeline.
2. Ensure that the GitHub workflows and actions are tested for validity before changes are merged or pushed.

Attention:

make sure the workflows of the workspace .github/workflows as well as the templates exasol/toolbox/templates/github/workflows are checked

Potential Tools

• actionlint: A static checker for GitHub Actions workflow files.
• yamllint: A linter for YAML files.
• act: A tool to run GitHub Actions locally.

[ckunki]

The critical parts are covered in some related PRs of the past.

• Add an id to each step of the workflow templates #701
  • all workflows now use the special python-environment version for setting up Python
• Refactoring/686 output yaml values #687
  • ruamel-yaml loads & validates that the yamls are valid (does not check specific GitHub flavor) 

Details and deviations

• There's no dedicated nox session, but integration tests that check the workflows, instead.
  • test/integration/tools/workflow_integration_test.py
• Validation implemented with ruamel-yaml and by using the workflows directly in the PTB.
• and available as a pre-commit hook

Regarding tool act mentioned above:

• not well-maintained
• rather slow
• doesn't give much output indicating errors