ci: fix code formatting

[johannes-lindgren]

⚠️ Note this is a stacked pull request that should only be merged after the base branch has been merged to main.

Fix all code formatting issues, so that we can require all automated checks to pass in the branch protection rules.

• Fix the code formatting in the .md and .yml files.
• .pnp.cjs and .pnp.loader.mjs are auto-generated by Yarn and are ignored by Git, and should thus be ignored by Prettier as well. Therefore, add a . prettierignore file where .pnp.* gets ignored