Fix typos in Doc/extending/extending.rst and Doc/library/shelve.rst (GH-136890)

Author: corneliusroemer

Doc/extending/extending.rst

@@ -214,7 +214,7 @@ and initialize it by calling :c:func:`PyErr_NewException` in the module's
 
    SpamError = PyErr_NewException("spam.error", NULL, NULL);
 
-Since :c:data:`!SpamError` is a global variable, it will be overwitten every time
+Since :c:data:`!SpamError` is a global variable, it will be overwritten every time
 the module is reinitialized, when the :c:data:`Py_mod_exec` function is called.
 
 For now, let's avoid the issue: we will block repeated initialization by raising an

Doc/library/shelve.rst

@@ -144,7 +144,7 @@ Restrictions
   which can cause hard crashes when trying to read from the database.
 
 * :meth:`Shelf.reorganize` may not be available for all database packages and
-  may temporarely increase resource usage (especially disk space) when called.
+  may temporarily increase resource usage (especially disk space) when called.
   Additionally, it will never run automatically and instead needs to be called
   explicitly.