[3.11] [3.12] gh-117347: Fix test_clinic side effects (GH-117363) (GH-117365) (#117366)

[3.12] gh-117347: Fix test_clinic side effects (GH-117363) (GH-117365)

gh-117347: Fix test_clinic side effects (GH-117363)

Save/restore converters in ClinicWholeFileTest and
ClinicExternalTest.

(cherry picked from commit c80d13838dbcfe239eeabfd950bc524d797e6db1)

Co-authored-by: Victor Stinner <vstinner@python.org>
(cherry picked from commit 35b6c4a4da201a947b2ceb96ae4c0d83d4d2df4f)

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