Sync pre-release CPython 3.15 branch from GitHub (2026-08-04)

Summary:
Imported python/cpython `3.15.0rc1+dev` from upstream rev [`eea1a49`](https://www.github.com/python/cpython/commit/eea1a49f690a3c9c49a27fee9a1935c5b4ed54f2) (committed 2026-08-04 13:41:23+00:00).

# Commit Info

- Base: (`3.15.0b4+dev`) - [`5bc7459`](https://www.github.com/python/cpython/commit/5bc7459474b7d3391b1d566f83728d8822654d1a) (commit date: 2026-08-03 21:21:11+00:00)
- Imported: (`3.15.0rc1+dev`) - [`eea1a49`](https://www.github.com/python/cpython/commit/eea1a49f690a3c9c49a27fee9a1935c5b4ed54f2) (commit date: 2026-08-04 13:41:23+00:00)

# Noteworthy file changes

- Low-signal files (1 added, 78 removed) (NEWS.d, docs, .github)

Complete list of added/removed files: https://www.internalfb.com/intern/everpaste/?color=0&handle=GOq5tScxLyJxXgYGAOsYkTBoNJV6br0LAAAz

Differential Revision: D114836942

fbshipit-source-id: 88d033daabeaac04aac9f0e52c74113b897aa651

Author: generatedunixname1734921407115435

cinderx/Interpreter/3.15/Includes/generated_cases.c.h

@@ -12873,8 +12873,21 @@
             _PyStackRef v;
             v = stack_pointer[-1];
             set = stack_pointer[-2 - (oparg-1)];
+            PyObject *set_o = PyStackRef_AsPyObjectBorrow(set);
+            if (!PySet_CheckExact(set_o)) {
+                _PyFrame_SetStackPointer(frame, stack_pointer);
+                _PyErr_Format(tstate, PyExc_TypeError,
+                              "'%T' object is not a set", set_o);
+                stack_pointer = _PyFrame_GetStackPointer(frame);
+                stack_pointer += -1;
+                ASSERT_WITHIN_STACK_BOUNDS(__FILE__, __LINE__);
+                _PyFrame_SetStackPointer(frame, stack_pointer);
+                PyStackRef_CLOSE(v);
+                stack_pointer = _PyFrame_GetStackPointer(frame);
+                JUMP_TO_LABEL(error);
+            }
             _PyFrame_SetStackPointer(frame, stack_pointer);
-            int err = _PySet_AddTakeRef((PySetObject *)PyStackRef_AsPyObjectBorrow(set),
+            int err = _PySet_AddTakeRef((PySetObject *)set_o,
                                         PyStackRef_AsPyObjectSteal(v));
             stack_pointer = _PyFrame_GetStackPointer(frame);
             if (err) {