Upgrade to yarn v4 with yarnPath

[shakuzen]

Specifies the package manager (yarn) and version (4.0.2) in package.json. The package-lock.json file was removed. Yarn reported an error due to having both it and yarn.lock. There should only be one lock file. The yarn.lock file has been rewritten in the latest yarn lock format.

https://yarnpkg.com/migration/guide

[shakuzen]

I'd like to get CI builds setup before merging this. Over the weekend, I noticed in a side project that the version of Yarn I expected to be used wasn't (JapanFinance/JapanFinance.github.io#47). We'll need to do something similar here I expect.

[shakuzen]

As suspected, this wasn't using yarn v4 but rather the globally installed yarn v1. From the build:

Run actions/setup-node@v4
Found in cache @ /opt/hostedtoolcache/node/20.9.0/x64
Environment details
/usr/local/bin/yarn --version
1.22.19

[shakuzen]

Having both a package-lock.json and yarn.lock file results in a warning from yarn. This file won't be used so long as yarn is doing the building. But I notice that GitHub is opening pull requests to update dependencies that only update package-lock.json. That won't actually change anything for our build.

warning package-lock.json found. Your project contains lock files generated by tools other than Yarn. It is advised not to mix package managers in order to avoid resolution inconsistencies caused by unsynchronized lock files. To clear this warning, remove package-lock.json.