prefer explicit utf8 for old pdflatex;

--- a/src/Doc/Demo_LIPIcs/document/root.tex	Fri Nov 04 19:59:00 2022 +0100
+++ b/src/Doc/Demo_LIPIcs/document/root.tex	Fri Nov 04 20:02:54 2022 +0100
@@ -1,4 +1,5 @@
 \documentclass[a4paper,UKenglish,cleveref,autoref]{lipics-v2021}
+\usepackage[utf8]{inputenc}
 
 \usepackage{isabelle,isabellesym}
 \isabellestyle{it}