doc: Update copyright notice in the documentation

Update copyright notice to reflect current year.
Fixes zephyrproject-rtos#54763.

Signed-off-by: Benjamin Cabé <[email protected]>

Author: kartben

doc/conf.py

@@ -36,7 +36,7 @@
 # -- Project --------------------------------------------------------------
 
 project = "Zephyr Project"
-copyright = "2015-2022 Zephyr Project members and individual contributors"
+copyright = "2015-2023 Zephyr Project members and individual contributors"
 author = "The Zephyr Project Contributors"
 
 # parse version from 'VERSION' file