Fix crash when parsing date

I was getting a `ValueError: Invalid isoformat string:
'2023-09-23T13:07:50'` crash.

toot/entities.py

@@ -6,6 +6,7 @@
 
 from dataclasses import dataclass, is_dataclass
 from datetime import date, datetime
+from dateutil import parser
 from typing import Dict, List, Optional, Type, TypeVar, Union
 from typing import get_type_hints
 
@@ -394,7 +395,7 @@ def _convert(field_type, value):
         return datetime.strptime(value, "%Y-%m-%dT%H:%M:%S.%f%z")
 
     if field_type == date:
-        return date.fromisoformat(value)
+        return parser.parse(value)
 
     if get_origin(field_type) == list:
         (inner_type,) = get_args(field_type)