pythongh-135956: Remove duplicate word in _pydatetime docstring (pythonGH-135957)

_pydatetime.isoformat docstring repeats 'giving'.
(cherry picked from commit e3ea6f2)

Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>

Author: terryjreedy

Lib/_pydatetime.py

@@ -2044,7 +2044,7 @@ def isoformat(self, sep='T', timespec='auto'):
         By default, the fractional part is omitted if self.microsecond == 0.
 
         If self.tzinfo is not None, the UTC offset is also attached, giving
-        giving a full format of 'YYYY-MM-DD HH:MM:SS.mmmmmm+HH:MM'.
+        a full format of 'YYYY-MM-DD HH:MM:SS.mmmmmm+HH:MM'.
 
         Optional argument sep specifies the separator between date and
         time, default 'T'.