`allow-newer: ^all` doesn't parse

```rst
-- Disregard all `^>=`-style upper bounds when dependency solving
allow-newer: ^all
```
SOURCE: [project allow-newer](https://cabal.readthedocs.io/en/latest/cabal-project-description-file.html#cfg-field-allow-newer)

The docs mention using `allow-newer: ^all` but trying this gives a parser error.

```
$ cabal init allow-any-newer --non-interactive
Warning: this is a debug build of cabal-install with assertions enabled.
[Info] Guessing dependencies...
[Info] Using cabal specification: 3.0
[Warn] unknown license type, you must put a copy in LICENSE yourself.
[Info] Creating fresh file CHANGELOG.md...
[Info] Creating fresh directory ./app...
[Info] Creating fresh file app/Main.hs...
[Info] Creating fresh file allow-any-newer.cabal...
[Warn] No synopsis given. You should edit the .cabal file and add one.
[Info] You may want to edit the .cabal file and add a Description field.

$ cd allow-any-newer/

$ cabal build all --enable-tests --enable-benchmarks
Warning: this is a debug build of cabal-install with assertions enabled.
Resolving dependencies...
Build profile: -w ghc-9.10.1 -O1
...

$ echo "allow-newer: all" > cabal.project.local

$ cabal build all --enable-tests --enable-benchmarks
Warning: this is a debug build of cabal-install with assertions enabled.
Resolving dependencies...
Up to date

$ echo "allow-newer: ^all" > cabal.project.local

$ cabal build all --enable-tests --enable-benchmarks
Warning: this is a debug build of cabal-install with assertions enabled.
Error: [Cabal-7090]
Error parsing project local configuration file /.../allow-any-newer/cabal.project.local:1:
"" (line 1, column 1):
unexpected "^"
expecting comma or "*"
```

I see the same behaviour with `cabal-install-3.12.1.0` and with `cabal-install` installed from d988732a2ad03b35a749af5940743cb9c9ca7035.