This was not done through `./mach lint`, `ruff` version `0.0.237` was called directly on the root directory with a modified `pyproject.toml` that only enabled the `UP016` rule with `--fix`. Some manual corrections were made after the auto fix ran to resolve incorrect behavior. No manual removals of `six` usages was done in this revision. Differential Revision: https://phabricator.services.mozilla.com/D245270