Attempting to run pull with custom build scripts failing

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- [X] I have checked to see if my question is addressed in the [FAQ](https://github.com/aws-amplify/amplify-hosting/blob/master/FAQ.md).
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### App Id

ddkfcre2qrht6

### AWS Region

us-east-1

### Amplify Hosting feature

Build settings

### Question
I am having trouble building on Amplify hosting using custom build scripts in amplify.yml. The script always gets hung up on whatever command I use before amplify pull. I need pull to bring in the aws-exports.js file and a post-pull script to run in order to modify that file. I have not even been able to get pull to run in the build process. Here is an example of the yml in one attempt:

```
version: 5
backend:
phases:
preBuild:
commands:
- npm config set //registry.npmjs.org/:_authToken=${NPM_AUTH_TOKEN}
- echo "@pqina:registry=https://npm.pqina.nl/" >> .npmrc
- echo "//npm.pqina.nl/:_authToken=${PQINA_NPM_TOKEN}" >> .npmrc
- npm i
build:
commands:
- echo "running build backend..."
- amplify pull --appId ddkfcre2qrht6 --envName test --yes
- echo "hello"
frontend:
phases:
build:
commands:
- npm run build
artifacts:
baseDirectory: .next
files:
- '**/*'
cache:
paths:
- node_modules/**/*
```

Start with the amplify.yml build settings and reproduce the backend phase containing npm i and amplify pull --appId ddkfcre2qrht6 --envName test --yes. Check where the command hangs and whether the build environment can create aws-exports.js before the post-pull modification. Done means the pull completes and the following commands run successfully.

Written by the indexing model from the issue text.