`yarn install` fails in `graph init` in pnpm workspace

[YaroShkvorets]

As reported by @cmwhited initing a subgraph in pnpm workspace fails when packageManager is set:

✖ Failed to install dependencies: Command failed: yarn
This project is configured to use pnpm because /Users/chris.whited/dev/chris.whited/ondo-tracker/package.json has a "packageManager" field

    Error: Command failed: yarn
    This project is configured to use pnpm because /Users/chris.whited/dev/chris.whited/ondo-tracker/package.json has a "packageManager" field

    Code: 1

Works if running pnpm install later though