Fix #7340 by correclty computing function name for push event (#7341)

* Add a failing test for issue #7340

If any delay occurs after "message.event" assignation in
LiveQueryServer._onAfterSave, the next subscription or request with a different
event might overwrite it, and by that using the wrong "push" function name.

* Remove updade of message and use res.event instead

This prevent computing function name from a
incorrect event if multiple subscriptions override
one by one the message.event.

* Update CHANGELOG.md

* Replace setTimeout by async/await expressions

spec/helper.js

@@ -515,3 +515,5 @@ jasmine.restoreLibrary = function (library, name) {
   }
   require(library)[name] = libraryCache[library][name];
 };
+
+jasmine.timeout = t => new Promise(resolve => setTimeout(resolve, t));