fix(embroider): add missing dependency to @ember/string

package.json

@@ -35,6 +35,7 @@
   },
   "dependencies": {
     "@ember/render-modifiers": "^2.0.4",
+    "@ember/string": "^3.0.0",
     "@embroider/util": "^1.5.0",
     "@glimmer/component": "^1.0.4",
     "@glimmer/tracking": "^1.0.4",

yarn.lock

@@ -1203,6 +1203,13 @@
     ember-cli-babel "^7.26.11"
     ember-modifier-manager-polyfill "^1.2.0"
 
+"@ember/string@^3.0.0":
+  version "3.0.0"
+  resolved "https://registry.yarnpkg.com/@ember/string/-/string-3.0.0.tgz#e3a3cc7874c9f64eadfdac644d8b1238721ce289"
+  integrity sha512-T+7QYDp8ItlQseNveK2lL6OsOO5wg7aNQ/M2RpO8cGwM80oZOnr/Y35HmMfu4ejFEc+F1LPegvu7LGfeJOicWA==
+  dependencies:
+    ember-cli-babel "^7.26.6"
+
 "@ember/[email protected]":
   version "2.6.0"
   resolved "https://registry.yarnpkg.com/@ember/test-helpers/-/test-helpers-2.6.0.tgz#d687515c6ab49ba72717fc62046970ef4a72ea9c"