Fix typo in Lib/typing.py (GH-19717)

Author: nfishe

Lib/typing.py

@@ -975,7 +975,7 @@ def _no_init(self, *args, **kwargs):
 
 
 def _allow_reckless_class_cheks():
-    """Allow instnance and class checks for special stdlib modules.
+    """Allow instance and class checks for special stdlib modules.
 
     The abc and functools modules indiscriminately call isinstance() and
     issubclass() on the whole MRO of a user class, which may contain protocols.