Merge pull request galaxyproject#16625 from bernt-matthias/doc/select…

…-multiple-default

Explicitly document default of multiple

lib/galaxy/tool_util/xsd/galaxy.xsd

@@ -3646,7 +3646,7 @@ drop-down menu select list. Used only when the ``type`` attribute value is
             <xs:documentation xml:lang="en">Allow multiple values to be
 selected. ``select`` parameters with ``multiple="true"`` are optional by
 default. Used only when the ``type`` attribute value is ``data``, ``group_tag``,
-or ``select``.</xs:documentation>
+or ``select``. Default is ``false``</xs:documentation>
           </xs:annotation>
         </xs:attribute>
         <xs:attribute name="numerical" type="PermissiveBoolean">