Fix memory leak
Fix memory leak

Some [Linux manpages][1] state

> This function makes copies of the strings pointed to by name and
> value (by contrast with putenv(3)).

and the [OpenGroup][2] manpage also states that the strings are
copied, so indeed they can and should be freed afterwards.

[1]: https://man7.org/linux/man-pages/man3/setenv.3.html
[2]: https://pubs.opengroup.org/onlinepubs/009695399/functions/setenv.html

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