fix: correct return variable in github backend

convert GitHub id into string to avoid TypeError

Author: melanger

src/satosa/backends/github.py

@@ -108,4 +108,4 @@ def user_information(self, access_token):
         r = requests.get(url, headers=headers)
         ret = r.json()
         ret['id'] = str(ret['id'])
-        return r.json()
+        return ret