erp5_web: authenticate cache should send Last-Modified

  Since we issue an no-store and no 304s, the Last-Modified could confuse the frontend if If-Modified-Since header is present on the request.

  If-Modified-Since is sent, the ERP5 wont return with 304, so we don't expect that the frontend does it (but it does), so since we don't expect that user stores the last request it makes no sense to return with Last-Modified.

bt5/erp5_web/ToolTemplateItem/caching_policy_manager.xml

@@ -81,7 +81,7 @@
                             </item>
                             <item>
                                 <key> <string>_last_modified</string> </key>
-                                <value> <int>1</int> </value>
+                                <value> <int>0</int> </value>
                             </item>
                             <item>
                                 <key> <string>_max_age_secs</string> </key>