GitHub Actions build fails due to missing puppeteer cache

[chrispcampbell]

Puppeteer 19.x included a change to the default cache location that breaks our GitHub Actions builds:
https://pptr.dev/guides/configuration#changing-the-default-cache-directory

Puppeteer itself uses the following cache step:
https://github.com/puppeteer/puppeteer/blob/main/.github/workflows/ci.yml#L159

I'm going to downgrade to Puppeteer 18.x for the time being, and will revisit with proper cache change in a later issue.

[chrispcampbell]

Reopening, need to add an explicit install step for the time being, will revisit with proper caching in a later issue.