bpo-37116: Use PEP 570 syntax for positional-only parameters. (GH-13700)

diff --git a/Lib/contextlib.py b/Lib/contextlib.py
index de989a0..94dc2bf 100644
--- a/Lib/contextlib.py
+++ b/Lib/contextlib.py
@@ -377,8 +377,7 @@
         return MethodType(cm_exit, cm)
 
     @staticmethod
-    def _create_cb_wrapper(*args, **kwds):
-        callback, *args = args
+    def _create_cb_wrapper(callback, /, *args, **kwds):
         def _exit_wrapper(exc_type, exc, tb):
             callback(*args, **kwds)
         return _exit_wrapper
@@ -553,8 +552,7 @@
         return MethodType(cm_exit, cm)
 
     @staticmethod
-    def _create_async_cb_wrapper(*args, **kwds):
-        callback, *args = args
+    def _create_async_cb_wrapper(callback, /, *args, **kwds):
         async def _exit_wrapper(exc_type, exc, tb):
             await callback(*args, **kwds)
         return _exit_wrapper