coq-paco for rocq 9.1

The current version of coq-paco, `coq-paco.4.2.3`, seems to build just fine in rocq 9.1, but its opam forbids this:
```
  "coq" {>= "8.13" & < "9.1~"}
```
Can I suggest that someone can just bump the `depends` to 9.2?
@gilhur 