Groups not dropped before running subprocess when using empty 'extra_groups' parameter

An issue was found in CPython 3.12.0 subprocess module on POSIX platforms. The issue was fixed in CPython 3.12.1 and does not affect other stable releases.

When using the extra_groups= parameter with an empty list as a value (ie extra_groups=[]) the logic regressed to not call setgroups(0, NULL) before calling exec(), thus not dropping the original processes' groups before starting the new process. There is no issue when the parameter isn't used or when any value is used besides an empty list.

This issue only impacts CPython processes run with sufficient privilege to make the setgroups system call (typically root).