erp5_officejs_eci_directory: Set missing http cache settings

bt5/erp5_officejs_eci_directory/SkinTemplateItem/portal_skins/erp5_officejs_european_cloud_industry/css/flag-icons.css.xml

@@ -6,6 +6,10 @@
     </pickle>
     <pickle>
       <dictionary>
+        <item>
+            <key> <string>_Cacheable__manager_id</string> </key>
+            <value> <string>http_cache</string> </value>
+        </item>
         <item>
             <key> <string>__name__</string> </key>
             <value> <string>flag-icons.css</string> </value>