Remove use of deprecated corepack

[runspired]

corepack was recently deprecated, as no one remaining on the nodejs core team wishes to continue maintaining it (the original author of it and only contributor to it has left the project).

it's also buggy, especially when it comes to pnpm install. I discovered we were using it for this repo when working to automate docs previews for ember-data.

$ node generate-local.js --project ember-data --version "5.4.0"
Running 'corepack' in ../data
/Users/cthoburn/.volta/tools/image/node/22.3.0/lib/node_modules/corepack/dist/lib/corepack.cjs:22460
    throw new Error(`Cannot find matching keyid: ${JSON.stringify({ signatures, keys })}`);

googling tells me I can work around this particular bug by telling corepack to ignore integrity checks entirely if pnpm is in use, but since we also shouldn't be using corepack anymore I figured I'd open an issue.

[mansona]

so this isn't actually true, corepack is not deprecated they just voted to not include it in the default node installation.

That specific issue that you're seeing is because you don't have a new enough version of corepack installed, just install it globally with either npm i -g corepack or pnpm i -g corepack or whatever you need 👍

[runspired]

@mansona actually I have the latest installed (because I'm using the version that comes via latest node, I don't actually have it installed at all), the issue is that corepack cannot verify any package manager distributed via npm (like pnpm is). Its an open issue, I worked around it by telling it to not verify.