Fix mypy error

Fix the following error caused by recent typing support.

oslo_log/formatters.py:185:12: error: Redundant cast to "str"
[redundant-cast]

Change-Id: Iaf735ef4756d6180839756ef9958e6ab7b9b7774
Signed-off-by: Takashi Kajinami <kajinamit@oss.nttdata.com>

oslo_log/formatters.py

@@ -22,7 +22,7 @@ import socket
 import sys
 import traceback
 from types import TracebackType
-from typing import Any, cast, TypeAlias, TypedDict
+from typing import Any, TypeAlias, TypedDict
 
 from dateutil import tz
 
@@ -182,7 +182,7 @@ def _json_dumps_with_fallback(obj: Any) -> str:
     # especially when the code using logs is not aware that the
     # JSONFormatter will be used.
     convert = functools.partial(jsonutils.to_primitive, fallback=repr)
-    return cast(str, jsonutils.dumps(obj, default=convert))
+    return jsonutils.dumps(obj, default=convert)
 
 
 class JSONLogRecord(TypedDict):