Google at this point favours long form content for many search intents. Being able to generate thousands of these pages in one-click is a real problem. Not just because of popular topics e.g. "covid-19 symptoms" but more so for the long tail e.g. "should I drink coffee to cure covid-19".
It may be that Google's algorithms don't care at all how human-like the text is, or that their own recognition algorithm/NN (whatever they use) isn't fooled. Even if it is affected, Google has the money and corpus to build its own competing NN to recognize GPT-3 text.
That said, there might be a different threat to Google. GPT-3 seems really useful as a search engine of sorts (with the first answer implementing the 'I'm Feeling Lucky' button). Tune it for a query syntax, and for getting the 'top X' results somehow, then we just need the web corpus and a basic filter over the results. We could have a very interesting Google competitor.
However, if the output needs to be curated and edited by humans, the scale and automation is gone - we just get a different manual process, with a modest improvement to speed at cost of some decline in quality, and that's not very impactful.