replace yapf reference with instruction to use 'ruff format'

[sjvrijn]

Checklist before requesting a review

• I have read the contribution guidelines
• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• [ ] All user facing changes have been added to CHANGELOG.md

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

List of related issues or pull requests**

Refs:

• Is yapf reference in README.dev.md outdated? #588

Describe the changes made in this pull request

Removed the reference to yapf for formatting code, and replaced it with an instruction to use ruff format instead.