Add @ember/test-waiters to app-template

Author: NullVoxPopuli

pnpm-lock.yaml

@@ -27,6 +27,7 @@
     "@ember/optional-features": "^2.0.0",
     "@ember/string": "^3.0.1",
     "@ember/test-helpers": "^3.3.0",
+    "@ember/test-waiters": "^3.1.0",
     "@embroider/test-setup": "^4.0.0",
     "@glimmer/component": "^1.1.2",
     "@glimmer/tracking": "^1.1.2",