docs(firebase_messaging): update index.html example of web background setup (#7366)
docs(firebase_messaging): update index.html example of web background setup (#7366)

Co-authored-by: Mike Diarmid <09bd5c7d87612a88198fdba2e685d07b6f84767b@gmail.com>
firebase/flutterfire,firebase/flutterfire,firebase/flutterfire,firebase/flutterfire,firebase/flutterfire,firebase/flutterfire,firebase/flutterfire,firebase/flutterfire,firebase/flutterfire,firebase/flutterfire