Standardize YAML format

[jakob-keller]

          yeah, that's why there should be a shared config so that every PR author wouldn't reformat by accident. I usually have yamllint wired via the pre-commit.com tool

Originally posted by @webknjaz in #1163 (comment)

[webknjaz]

$ cat .yamllint
---

extends: default

rules:
  indentation:
    level: error
    indent-sequences: false
  truthy:
    allowed-values:
    - >-
      false
    - >-
      true
    - >-  # Allow "on" key name in GHA CI/CD workflow definitions
      on

...