Fixed: multiple attribute removed in dropdown macro (OFBIZ-12127)

This set back the multiple attribute for multi dropdown to be displayed
correctly

themes/common-theme/template/macro/HtmlFormMacroLibrary.ftl

@@ -167,6 +167,7 @@ under the License.
     <select name="${name?default("")}"
       <@renderClass className alert /> <@renderDisabled disabled />
       <#if id?has_content> id="${id}"</#if>
+      <#if multiple?has_content> multiple="multiple"</#if>
       <#if ajaxEnabled> class="autoCompleteDropDown"</#if>
       <#if event?has_content> ${event}="${action}"</#if>
       <#if size?has_content> size="${size}"</#if>