create release modifications for version 4.1.1

see https://icalendar.readthedocs.io/en/latest/maintenance.html#

CHANGES.rst

@@ -2,7 +2,7 @@ Changelog
 =========
 
 
-4.1.1 (unreleased)
+4.1.1 (2023-09-06)
 ------------------
 
 Bug fixes:

src/icalendar/__init__.py

@@ -1,5 +1,5 @@
 # -*- coding: utf-8 -*-
-__version__ = '4.1.1.dev0'
+__version__ = '4.1.1'
 
 from icalendar.cal import (
     Calendar,