Update dependency ember-cli-notifications to v9

Author: renovate[bot]

ember/package.json

@@ -59,7 +59,7 @@
     "ember-cli-htmlbars": "5.7.1",
     "ember-cli-inject-live-reload": "2.0.2",
     "ember-cli-mirage": "2.1.0",
-    "ember-cli-notifications": "6.3.4",
+    "ember-cli-notifications": "9.0.0",
     "ember-cli-sass": "10.0.1",
     "ember-cli-uglify": "3.0.0",
     "ember-click-outside": "2.0.0",