Autodetect output format based on environment variables.

[MichaReiser]

a thought: instead of needing to set RUFF_OUTPUT_FORMAT: github in GitHub Actions, ruff could check the env var GitHub itself sets and use the correct output format:

GITHUB_ACTIONS: Always set to true when GitHub Actions is running the workflow. You can use this variable to differentiate when tests are being run locally or by GitHub Actions.

similarly, GitLab sets GITLAB_CI. Azure isn't so clearcut, maybe TF_BUILD

Originally posted on discord (link)

[Avasam]

As long as it can still be overridden, having a smart dynamic default sounds like a nice improvement.