[3.13] gh-143309: fix UAF in `os.execve` when the environment is concurrently mutated (GH-143314) (#143431)

[3.13] gh-143309: fix UAF in `os.execve` when the environment is concurrently mutated (GH-143314) (#143431)

(cherry picked from commit 9609574e7fd36edfaa8b575558a82cc14e65bfbc)
(cherry picked from commit c99f7667436d8978b4077704333e2a351f2a026f)