gh-116938: Fix dict.update docstring and remove erraneous full stop from dict documentation (#125421)

Co-authored-by: Adam Turner <[email protected]>

Author: Prometheus3375

Doc/library/stdtypes.rst

@@ -4674,7 +4674,7 @@ can be used interchangeably to index the same dictionary entry.
 
       :meth:`update` accepts either another object with a ``keys()`` method (in
       which case :meth:`~object.__getitem__` is called with every key returned from
-      the method). or an iterable of key/value pairs (as tuples or other iterables
+      the method) or an iterable of key/value pairs (as tuples or other iterables
       of length two). If keyword arguments are specified, the dictionary is then
       updated with those key/value pairs: ``d.update(red=1, blue=2)``.
 

Objects/dictobject.c

@@ -4673,8 +4673,8 @@ PyDoc_STRVAR(getitem__doc__,
 "__getitem__($self, key, /)\n--\n\nReturn self[key].");
 
 PyDoc_STRVAR(update__doc__,
-"D.update([E, ]**F) -> None.  Update D from dict/iterable E and F.\n\
-If E is present and has a .keys() method, then does:  for k in E: D[k] = E[k]\n\
+"D.update([E, ]**F) -> None.  Update D from mapping/iterable E and F.\n\
+If E is present and has a .keys() method, then does:  for k in E.keys(): D[k] = E[k]\n\
 If E is present and lacks a .keys() method, then does:  for k, v in E: D[k] = v\n\
 In either case, this is followed by: for k in F:  D[k] = F[k]");