chore(deps): update dependency @ember/test-helpers to v2.9.3

Author: renovate[bot]

package.json

@@ -39,7 +39,7 @@
   },
   "devDependencies": {
     "@ember/optional-features": "2.0.0",
-    "@ember/test-helpers": "2.2.6",
+    "@ember/test-helpers": "2.9.3",
     "@embroider/test-setup": "0.41.0",
     "@glimmer/component": "1.0.4",
     "@glimmer/tracking": "1.0.4",