fix: correct the build process for v6.47.0+

[jnsgruk]

This makes a couple of changes to address an issue with recent versions:

• Use the same version of NPM and Yarn as the upstream CI
• Stop patching the package.json to build to directory, use new flags

[popey]

Tested on my local machine, building from this PR in lxd. Installed 6.47.0 and it worked fine.