[3.14] gh-142353: Isolate tests from personal GNU Readline init files (GH-142370) (#142634)

gh-142353: Isolate tests from personal GNU Readline init files (GH-142370)

Isolate tests from personal Readline init files using `INPUTRC=/dev/null` trick.
(cherry picked from commit f564654bae79c69e3de40dadbec2399f1423ffcf)

Co-authored-by: Bartosz Sławecki <bartosz@ilikepython.com>
Co-authored-by: Victor Stinner <vstinner@python.org>