Even though Composer v2 was being pulled from the Composer Docker image,
Composer v1 was still being used.
Because I've added the `/app/bin` path to `$PATH`, a version in
`/app/bin/composer` was being used. The simplest way that I can fix
this is re-ordering the variable so that the path is added after the
originals and the Composer version in `/usr/bin/composer` is used.
