chore(deps): update dependency @ember/string to v4

Author: renovate[bot]

docs-app/package.json

@@ -33,7 +33,7 @@
     "@docfy/core": "^0.8.0",
     "@docfy/ember": "^0.8.5",
     "@ember/optional-features": "^2.0.0",
-    "@ember/string": "^3.1.1",
+    "@ember/string": "^4.0.0",
     "@ember/test-helpers": "^3.2.0",
     "@embroider/compat": "^3.0.0",
     "@embroider/core": "^3.0.0",