fix: update type hinting for Workflow import in model.py

Signed-off-by: -LAN- <laipz8200@outlook.com>

api/models/model.py

@@ -4,7 +4,7 @@ import uuid
 from collections.abc import Mapping
 from datetime import datetime
 from enum import Enum, StrEnum
-from typing import Any, Literal, Optional
+from typing import TYPE_CHECKING, Any, Literal, Optional
 
 import sqlalchemy as sa
 from flask import request
@@ -18,12 +18,15 @@ from core.file import helpers as file_helpers
 from core.file.tool_file_parser import ToolFileParser
 from libs.helper import generate_string
 from models.enums import CreatedByRole
-from models.workflow import Workflow, WorkflowRunStatus
+from models.workflow import WorkflowRunStatus
 
 from .account import Account, Tenant
 from .engine import db
 from .types import StringUUID
 
+if TYPE_CHECKING:
+    from .workflow import Workflow
+
 
 class DifySetup(db.Model):
     __tablename__ = "dify_setups"