fix(deps): update dependency execa to v4

Author: renovate-bot

package.json

@@ -46,7 +46,7 @@
     "broccoli-stew": "^3.0.0",
     "debug": "^4.0.0",
     "ember-cli-babel-plugin-helpers": "^1.0.0",
-    "execa": "^3.0.0",
+    "execa": "^4.0.0",
     "fs-extra": "^9.0.1",
     "resolve": "^1.5.0",
     "rsvp": "^4.8.1",