Use u'' instead of '' in libgdiagnostics/conf.py

Use u'' instead of '' in libgdiagnostics/conf.py

libgdiagnostics/conf.py breaks update-copyright.py --this-year,
which only accepts copyright year in u'' literals in python files,
not in ''.

2025-01-02  Jakub Jelinek  <jakub@redhat.com>

	* doc/libgdiagnostics/conf.py: Use u'' instead of '' in
	project and copyright initialization.