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

[picnixz]

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

• Issue: gh-143309

[bedevere-bot]

:robot: New build scheduled with the buildbot fleet by @picnixz for commit 2c3879cb92836a533dff7622e5c321ac2a686126 :robot:

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F143431%2Fmerge

If you want to schedule another build, you need to add the :hammer: test-with-buildbots label again.