[greenlet] Fix for Python 3.13 (#13648)

`get_tstate_trash_delete_nesting()` is not available
on Python 3.13.

Author: srittau

stubs/greenlet/greenlet/_greenlet.pyi

@@ -1,3 +1,4 @@
+import sys
 from collections.abc import Callable
 from contextvars import Context
 from types import FrameType, TracebackType
@@ -71,7 +72,10 @@ def enable_optional_cleanup(enabled: bool, /) -> None: ...
 def get_clocks_used_doing_optional_cleanup() -> int: ...
 def get_pending_cleanup_count() -> int: ...
 def get_total_main_greenlets() -> int: ...
-def get_tstate_trash_delete_nesting() -> int: ...
+
+if sys.version_info < (3, 13):
+    def get_tstate_trash_delete_nesting() -> int: ...
+
 def getcurrent() -> greenlet: ...
 def gettrace() -> _TraceCallback | None: ...
 def set_thread_local(key: object, value: object, /) -> None: ...