active-repositories in cabal.project does not override cabal.config

**Describe the bug**
Running `ghc-wasm-meta`'s `setup.sh` script adds `active-repositories: hackage.haskell.org, head.hackage.haskell.org:override` to `~/.cabal/cabal.config` and runs `cabal update`.

In my project, I have `cabal.project` with `active-repositories: hackage.haskell.org`, but `cabal update` is still showing head.hackage. I would expect `active-repositories` in `cabal.project` to override `cabal.config`; is that assumption wrong? How do I prevent using head.hackage without patching the script to not set head.hackage?

**System information**
- Operating system
- `cabal`, `ghc` versions

**Additional context**
Add any other context about the problem here.