Fixed CVE-2023-36053 -- Prevented potential ReDoS in EmailValidator and URLValidator.

Thanks Seokchan Yoon for reports.

django/forms/fields.py

@@ -616,6 +616,9 @@ class EmailField(CharField):
     default_validators = [validators.validate_email]
 
     def __init__(self, **kwargs):
+        # The default maximum length of an email is 320 characters per RFC 3696
+        # section 3.
+        kwargs.setdefault("max_length", 320)
         super().__init__(strip=True, **kwargs)