Copy an example to PartialOrd as well
In https://github.com/rust-lang/rust/pull/88202 I added an example for deriving PartialOrd on enums, but only later did I realize that I actually put the example on Ord.
This copies the example to PartialOrd as well, which is where I intended for it to be.
We could also delete the example on Ord, but I see there's already some highly similar examples shared between Ord and PartialOrd, so I figured we could leave it.
I also changed some type annotations in an example from `x : T` to the more common style (in Rust) of `x: T`.
775fe37ca9