Ensure a minimum of 4GB of RAM on CI hosts?

[targos]

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2GB is usually not enough to compile V8 and we have to restart CI jobs until they pass (thanks to ccache)

I'd like to upgrade the recent DO hosts that I created to 4GB instead of 2GB.

Another option could be to enable swap, but I suppose we prefer to avoid that if we can to avoid slowing down jobs?

Refs: https://github.com/nodejs/build/pull/3557