This work aims to make Linux builds faster to make https://github.com/ooni/probe/issues/2249 more convenient. Since those builds runs inside Docker, the problem to solve here is to save/restore the Go caches notwithstanding Docker. Because Docker runs as root, we need to modify the build a bit to run as a normal user. Otherwise, we will not be able to save the Go cache using actions/cache@v3. (Other approaches such as using `sudo` are possible but running the build as an unprivileged user actually looks cleaner, so I chose to do that.) While there, add a `.editorconfig`.
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