DEV: Add missing `pluginId` to a `modifyClass` test (#23265)

app/assets/javascripts/discourse/tests/unit/lib/plugin-api-test.js

@@ -105,6 +105,8 @@ module("Unit | Utility | plugin-api", function (hooks) {
     // This puts things in a state which will trigger https://github.com/emberjs/ember.js/issues/18860 when a native getter is overridden.
     withPluginApi("1.1.0", (api) => {
       api.modifyClass("test-class:main", {
+        pluginId: "plugin-api-test",
+
         get foo() {
           return "modified getter";
         },