[3.13] gh-121605: Increase timeout in test_pyrepl.run_repl (GH-121606) (#121702)

We also need to close the `slave_fd` earlier so that reading from
`master_fd` won't block forever when the subprocess finishes.
(cherry picked from commit abc3aeebdbae560476f2f8c0312e9a4bf0dbfd33)

Co-authored-by: Sam Gross <colesbury@gmail.com>