The nixos module uses `caddy fmt` to *format* the generated Caddyfile.
v2.6.3 slightly altered `caddy fmt`'s behavior.
Excerpt from https://github.com/caddyserver/caddy/releases/tag/v2.6.3
> cmd: caddy fmt return code is 1 if not formatted
> cmd: fmt exit successfully after overwriting config file
Which is why the internal `Caddyfile-formatted` now uses `cp` and `caddy fmt --overwrite` instead
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