[3.13] gh-121359: Run test_pyrepl in isolated mode (GH-121414) (#121417)

gh-121359: Run test_pyrepl in isolated mode (GH-121414)

run_repl() now pass the -I option (isolated mode) to Python if the
'env' parameter is not set.
(cherry picked from commit 6239d41527d5977aa5d44e4b894d719bc045860e)

Co-authored-by: Victor Stinner <vstinner@python.org>