Sync pre-release CPython main branch from GitHub (2026-03-06)

Summary:
Imported python/cpython `3.15.0a6+` from upstream rev [`c3fb0d9`](https://www.github.com/python/cpython/commit/c3fb0d9d96902774c08b199dda0479a8d31398a5) (committed 2026-03-06 00:42:41+00:00).

# Commit Info

Base: (`3.15.0a6+`) - [`6acaf65`](https://www.github.com/python/cpython/commit/6acaf659ef0fdee131bc02f0b58685da039b5855) (commit date: 2026-03-05 03:48:25+00:00)
Imported: (`3.15.0a6+`) - [`c3fb0d9`](https://www.github.com/python/cpython/commit/c3fb0d9d96902774c08b199dda0479a8d31398a5) (commit date: 2026-03-06 00:42:41+00:00)

# Files added

```
Misc/NEWS.d/next/Core_and_Builtins/2026-02-21-12-16-46.gh-issue-145055.VyT-zI.rst
Misc/NEWS.d/next/Library/2026-03-03-11-49-44.gh-issue-145417.m_HxIL.rst
Tools/wasm/emscripten/emscripten_version.txt
```

Differential Revision: D95505545

fbshipit-source-id: 2bfb4311562749de708e6ba23148b29833a58db7

Author: generatedunixname1734921407115435

cinderx/UpstreamBorrow/borrowed-3.15.gen_cached.c

@@ -781,7 +781,7 @@ dict_unhashable_type(PyObject *op, PyObject *key)
     }
 
     const char *errmsg;
-    if (PyObject_IsInstance(op, (PyObject*)&PyFrozenDict_Type)) {
+    if (PyFrozenDict_Check(op)) {
         errmsg = "cannot use '%T' as a frozendict key (%S)";
     }
     else {