Update dependency @ember/string to v4

Author: renovate[bot]

package.json

@@ -29,7 +29,7 @@
   },
   "devDependencies": {
     "@ember/optional-features": "2.1.0",
-    "@ember/string": "3.1.1",
+    "@ember/string": "4.0.0",
     "@ember/test-helpers": "3.3.0",
     "@embroider/test-setup": "3.0.3",
     "@glimmer/component": "1.1.2",