[3.14] gh-147998: Fix possible memory leak in _pop_preserved (crossinterp.c) (GH-147999) (GH-149365)

(cherry picked from commit 72f29dc)

Co-authored-by: Maurycy Pawłowski-Wieroński <maurycy@maurycy.com>

Author: miss-islington

Misc/NEWS.d/next/Core_and_Builtins/2026-04-02-13-25-09.gh-issue-147998.wnzkRT.rst

@@ -0,0 +1,3 @@
+Fixed a memory leak in interpreter helper calls so cleanup works when an
+operation falls across interpreter boundaries. Patch by Maurycy
+Pawłowski-Wieroński.

Python/crossinterp.c

@@ -2965,7 +2965,7 @@ _pop_preserved(_PyXI_session *session,
         *p_xidata = NULL;
     }
     else {
-        _PyXI_namespace *xidata = _create_sharedns(session->_preserved);
+        xidata = _create_sharedns(session->_preserved);
         if (xidata == NULL) {
             failure.code = _PyXI_ERR_PRESERVE_FAILURE;
             goto error;