gh-46927: Prevent readline from overriding environment

Misc/NEWS.d/next/Core_and_Builtins/2025-05-07-18-31-31.gh-issue-46927.sF02gj.rst

@@ -0,0 +1,2 @@
+Prevent readline from overriding COLUMNS and LINES environment variables, as
+values are not updated on terminal resize.

Modules/readline.c

@@ -1323,6 +1323,13 @@ setup_readline(readlinestate *mod_state)
     /* The name must be defined before initialization */
     rl_readline_name = "python";
 
+#if !defined(__APPLE__)
+    /* Prevent readline from changing environment variables such as LINES and
+     * COLUMNS.
+     */
+    rl_change_environment = 0;
+#endif
+
     /* the libedit readline emulation resets key bindings etc
      * when calling rl_initialize.  So call it upfront
      */