Tooling: use upstream danger-ruby-swiftformat version

We use [a fork](https://github.com/shiftyjelly/danger-ruby-swiftformat) of the [original `danger-ruby-swiftformat` plugin](https://github.com/garriguv/danger-ruby-swiftformat/).

Judging by the commit history in the fork we use, I'd say the reason was because the upstream version didn't support a SwiftFormat change. As far as I can see, that change [has now been supported](https://github.com/garriguv/danger-ruby-swiftformat/pull/33).

However, there's no urgent reason to switch, really, other than running on "official" tools.

Inspect the project's dependency and tooling configuration to find where the shiftyjelly danger-ruby-swiftformat fork is selected. Compare that declaration with the upstream danger-ruby-swiftformat repository and PR #33, then verify that the project uses the upstream plugin and its SwiftFormat support remains intact.

Written by the indexing model from the issue text.