Improve markup of unnest example

doc/src/sgml/func.sgml

@@ -10385,7 +10385,8 @@ SELECT NULLIF(value, '(none)') ...
         <entry><type>setof anyelement</type></entry>
         <entry>expand an array to a set of rows</entry>
         <entry><literal>unnest(ARRAY[1,2])</literal></entry>
-        <entry><literal>1</literal><para><literal>2</literal></para> (2 rows)</entry>
+        <entry><literallayout class="monospaced">1
+2</literallayout>(2 rows)</entry>
        </row>
       </tbody>
      </tgroup>