Address review comments

Author: markshannon

Include/internal/pycore_gc.h

@@ -244,8 +244,7 @@ static inline void _PyObject_GC_TRACK(
                           "object is in generation which is garbage collected",
                           filename, lineno, __func__);
 
-    PyThreadState *tstate = _PyThreadState_GET();
-    struct _gc_runtime_state *gcstate = &tstate->interp->gc;
+    struct _gc_runtime_state *gcstate = &_PyInterpreterState_GET()->gc;
     PyGC_Head *generation0 = &gcstate->young.head;
     PyGC_Head *last = (PyGC_Head*)(generation0->_gc_prev);
     _PyGCHead_SET_NEXT(last, gc);

Misc/NEWS.d/next/Core_and_Builtins/2025-10-17-18-03-12.gh-issue-139951.IdwM2O.rst

@@ -2,6 +2,6 @@ Fixes a regression in GC performance for a growing heap composed mostly of
 small tuples.
 
 *  Counts number of actually tracked objects, instead of trackable objects.
-   This ensures that untracking tuples has the desired effect of reducing GC overhead
+   This ensures that untracking tuples has the desired effect of reducing GC overhead.
 *  Does not track most untrackable tuples during creation.
    This prevents large numbers of small tuples causing excessive GCs.