Regex whitespace before character

Question

I'm looking for a check job to do before pushing commits. I have some json files that might not be properly formatted.

{
  "key": "good value.",
  "key2": "bad value. ",
   ...
}

I want to find which files contains a JSON key or value that contains a whitespace before the end of the double quote.

I tried :

find config/*.json -exec grep '\s(?=[^"\s]*")' {} \;

It does not get me any match but it works on https://www.regextester.com/ with the previous example. Any clue ?