Add @ember/test-waiters

Author: NullVoxPopuli

files/package.json

@@ -38,6 +38,7 @@
     "@babel/plugin-transform-typescript": "^7.25.2",<% } %>
     "@babel/runtime": "^7.25.6",
     "@ember/test-helpers": "^5.2.1",
+    "@ember/test-waiters": "^4.1.1",
     "@embroider/addon-dev": "^8.1.0",
     "@embroider/core": "^4.1.0",
     "@embroider/compat": "^4.1.0",