DEV: prevents route action to crash in tests (#28409)

`routeAction` is testing at runtime that a route exists when in debug mode. However in the case of components tested in isolation there's no existing route which was causing an exception, this commit prevents this check in this case as it's irrelevant.

app/assets/javascripts/discourse/app/helpers/route-action.js

@@ -5,6 +5,7 @@ import { assert, runInDebug } from "@ember/debug";
 import { computed, get } from "@ember/object";
 import { getOwner } from "@ember/owner";
 import { join } from "@ember/runloop";
+import { isTesting } from "discourse-common/config/environment";
 
 function getCurrentRouteInfos(router) {
   let routerLib = router._routerMicrolib || router.router;
@@ -30,6 +31,7 @@ function getRouteWithAction(router, actionName) {
 function routeAction(actionName, router, ...params) {
   assert("[ember-route-action-helper] Unable to lookup router", router);
 
+  if (!isTesting() || router.currentRoute) {
     runInDebug(() => {
       let { handler } = getRouteWithAction(router, actionName);
       assert(
@@ -37,6 +39,7 @@ function routeAction(actionName, router, ...params) {
         handler
       );
     });
+  }
 
   return function (...invocationArgs) {
     let { action, handler } = getRouteWithAction(router, actionName);