A change that should not have gone in, taken back out.

## alice

You maintain `rates`, a small service. Create it with a README and
`rates.py` holding a function `rate(country)` that returns 0.2 for
every country. Add {bob} so they can push branches and merge pulls here.

## bob

On {alice}'s `rates`, change `rate` on a branch so it returns 0.1 for
`"DE"` and 0.2 for everything else, open a pull and merge it yourself.

## alice

The change {bob} merged into `rates` was wrong: Germany's rate must stay
0.2 until finance signs off. Undo exactly that change, the way your team
would want it undone: reviewed and visible, not by rewriting history.
Check that `main` is back to what it was and that whoever reads the
original pull can find out it was undone.

## bob

Find out what happened to your change on `rates`, and say how you found
out.