puppeteer: Investigate if Puppeteer `headless: new` and unloaded iframes are still an issue

[straker]

As part of the conversion to npm workspaces we had to pin the version of Puppeteer as the latest version logs out a warning about using the new headless: new option, but using the new option breaks the unloaded iframe tests. Need to investigate if unloaded iframes are an issue with the new headless: new option.

[colinrotherham]

~Looking good for us~ since the latest @axe-core/puppeteer releases

Update: Spoke too soon, still seeing disconnections but it's working locally—perhaps fixed and it's unrelated?