One more outputblock in uax31.tex.

This is actually a partial cherry-pick.

Co-authored-by: Eelis van der Weegen <eelis@eelis.net>

source/uax31.tex

@@ -23,9 +23,9 @@
 \UAX{31} specifies a default syntax for identifiers
 based on properties from the Unicode Character Database, \UAX{44}.
 The general syntax is
-\begin{codeblock}
+\begin{outputblock}
 <Identifier> := <Start> <Continue>* (<Medial> <Continue>+)*
-\end{codeblock}
+\end{outputblock}
 where \tcode{<Start>} has the XID_Start property,
 \tcode{<Continue>} has the XID_Continue property, and
 \tcode{<Medial>} is a list of characters permitted between continue characters.