Yarn doesn't run build scripts nor respects GOOGLE_NODE_RUN_SCRIPTS

[shaikatzz]

Describe the bug
Using npm/pnpm the builder uses the DetermineBuildCommands function to determine which build commands the tool should run, if using yarn it runs only gcp-build which is not expected, and not documented

Additional context
How are you using GCP buildpacks?
pack and the gcr.io/buildpacks/builder

Did this used to work?
No
Was this working before? When did you start noticing these errors?

What language is your project primarily written in?
Node.js

Steps To Reproduce
Steps to reproduce the behavior:

1. pack build on a nodejs project with yarn.lock file, having a build script.

Expected behavior
It should run the build script

Actual behavior
It doesn't run the build script