pytest: use hmac.new instead of hmac.HMAC

According to documentation, hmac.new is the way to create a HMAC object ... and
the first argument is mandaatory and we don't want to name it.

This has no functional change but will address a pytype warning:

File "kallithea/model/user.py", line 304, in get_reset_password_token: Invalid keyword arguments (digestmod, key, msg) to function HMAC.__init__ [wrong-keyword-args]

kallithea/model/user.py

@@ -301,8 +301,8 b' class UserModel(object):'
         guaranteed not to occur in any of the values.
         """
         app_secret = config.get('app_instance_uuid')
-        return hmac.HMAC(
-            key='\0'.join([app_secret, user.password]).encode('utf-8'),
+        return hmac.new(
+            '\0'.join([app_secret, user.password]).encode('utf-8'),
             msg='\0'.join([session_id, str(user.user_id), user.email, str(timestamp)]).encode('utf-8'),
             digestmod=hashlib.sha1,
         ).hexdigest()