bpo-36799: Fix typo in ctypes.rst (pythonGH-13104)

Author: sehnsucht13

Doc/library/ctypes.rst

@@ -2376,7 +2376,7 @@ other data types containing pointer type fields.
  and so on). Later assignments to the :attr:`_fields_` class variable will
  raise an AttributeError.
 
- It is possible to defined sub-subclasses of structure types, they inherit
+ It is possible to define sub-subclasses of structure types, they inherit
  the fields of the base class plus the :attr:`_fields_` defined in the
  sub-subclass, if any.
 
@@ -2424,7 +2424,7 @@ other data types containing pointer type fields.
  td.lptdesc = POINTER(some_type)
  td.u.lptdesc = POINTER(some_type)
 
- It is possible to defined sub-subclasses of structures, they inherit the
+ It is possible to define sub-subclasses of structures, they inherit the
  fields of the base class. If the subclass definition has a separate
  :attr:`_fields_` variable, the fields specified in this are appended to the
  fields of the base class.