Correctly format predefined constant pages

Author: kocsismate

appendices/reserved.constants.core.xml

@@ -649,7 +649,7 @@
    <listitem>
     <simpara>
      A Windows
-     <keycombo action='simul'>
+     <keycombo action="simul">
       <keycap>CTRL</keycap>
       <keycap>C</keycap>
      </keycombo>
@@ -666,7 +666,7 @@
    <listitem>
     <simpara>
      A Windows
-     <keycombo action='simul'>
+     <keycombo action="simul">
       <keycap>CTRL</keycap>
       <keycap>BREAK</keycap>
      </keycombo>