[3.14] gh-142763: Fix race in ZoneInfo cache eviction (gh-144978) (#145781)

The cache may be cleared between the evaluation of the if statement and the
call to popitem.

(cherry picked from commit 665c1db94f46f8e1a18a8c2f89adb3bc72cb83dc)

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