gh-157170: Restore use_env() after test_use_prescr_screen in test_curses

curses.use_env() sets a process-wide ncurses default, not a property of
the screen it is called on. test_use_prescr_screen turned it off and
never turned it back on, so every newterm() in the rest of the process
took the screen size from terminfo alone. For a terminfo entry with no
size, such as "linux" on the CI runners, that makes newterm() return
NULL: test_curses failed with 138 errors in the parallel phase of every
Ubuntu CI run and only passed on the rerun, which skips ScreenTests.

Author: iamsharduld

Lib/test/test_curses.py

@@ -3459,6 +3459,10 @@ def test_use_prescr_screen(self):
             with self.assertRaises(curses.error):
                 prescr.use(func)
         # Affecting the state before initscr() is what such a screen is for.
+        # use_env() sets a process-wide default rather than a property of the
+        # screen it is called on, so restore it: with it off, newterm() has no
+        # size for a terminfo entry without one (such as "linux") and fails.
+        self.addCleanup(curses.use_env, True)
         prescr.use(lambda scr: curses.use_env(False))
         # The current screen is unchanged.
         screen.stdscr.refresh()

Misc/NEWS.d/next/Tests/2026-09-08-12-30-00.gh-issue-157170.510IJX.rst

@@ -0,0 +1,3 @@
+Fix ``test_curses`` failing with 138 errors when ``TERM`` names a terminfo
+entry without a size, such as ``linux`` on the CI runners:
+``test_use_prescr_screen`` now restores :func:`curses.use_env`.