WIP: Skip CI jobs if "[skip ci]" is in the commit message

[seisman]

Description of proposed changes

We don't run CI jobs for some tiny changes (e.g., typos). Like other CI services, if the commit message contains [skip ci], then the CI jobs (testing) should be skipped.

The solution comes from https://github.community/t/github-actions-does-not-respect-skip-ci/17325.

The solution above doesn't work. Currently, the github action variable github doesn't contain the commit message anymore.

Reminders

• Run make format and make check to make sure the code follows the style guide.
• Add tests for new features or tests that would have caught the bug that you're fixing.
• Add new public functions/methods/classes to doc/api/index.rst.
• Write detailed docstrings for all functions/methods.
• If adding new functionality, add an example to docstrings or tutorials.