DEV: Update `ember-qunit` (#17251)

app/assets/javascripts/discourse-widget-hbs/package.json

@@ -24,6 +24,7 @@
   "devDependencies": {
     "@ember/optional-features": "^2.0.0",
     "@glimmer/component": "^1.1.2",
+    "@glimmer/syntax": "^0.84.2",
     "broccoli-asset-rev": "^3.0.0",
     "ember-cli": "~3.25.3",
     "ember-cli-dependency-checker": "^3.3.1",

app/assets/javascripts/discourse/package.json

@@ -22,6 +22,7 @@
     "@ember/optional-features": "^2.0.0",
     "@ember/test-helpers": "^2.8.1",
     "@glimmer/component": "^1.1.2",
+    "@glimmer/syntax": "^0.84.2",
     "@glimmer/tracking": "^1.1.2",
     "@popperjs/core": "2.10.2",
     "@uppy/aws-s3": "^2.0.8",
@@ -53,7 +54,7 @@
     "ember-exam": "^7.0.1",
     "ember-export-application-global": "^2.0.1",
     "ember-load-initializers": "^2.1.1",
-    "ember-qunit": "^5.1.2",
+    "ember-qunit": "^5.1.5",
     "ember-rfc176-data": "^0.3.17",
     "ember-source": "~3.15.0",
     "ember-test-selectors": "^6.0.0",