In Go the answer is that strings are just some bytes, and filenames are just some bytes and so this naturally just works.
In Rust the answer is that strings are AsRef<Path> and you can open a Path, so when you call open the compiler gives it a Path even though that isn't what you actually had (you can't mutate the Path via this reference, so we know open doesn't change it).
The difference becomes more stark if we go the other way, starting from a list of files in the current directory and writing a JSON file.
In Go if you get a list of all the filenames in the current directory, it's a list of strings, and the fact that those aren't actually text is your problem, you will need to explicitly take care of this or you can't emit valid JSON.
In Rust, you get Paths, and you're going to need to explicitly ask for the strings to make JSON, at which point you have to decide what you want to do if the Path isn't just text, you're obliged to decide, even if it's just panic (ie abort the program).