set_key creates orphan .env file

set_key states "If the .env path given doesn't exist, fails instead of risking creating an orphan .env somewhere in the filesystem".

set_key has no check if the file exists. As it uses rewrite which if path passed is not a file, it creates an empty file.

if not os.path.isfile(path):
        with open(path, mode="w", encoding=encoding) as source:
            source.write("")

https://github.com/theskumar/python-dotenv/blob/3ffcef60d10813b72ecf85d5941d51b0207cd40e/src/dotenv/main.py#L134

Start with set_key and rewrite in src/dotenv/main.py, especially the file-existence behavior described in the issue. Reproduce set_key with a nonexistent .env path and inspect the related tests or test entry points. Done means a missing path fails without creating an orphan file, while existing-file behavior remains intact.