Fix PydanticModel type checking. (#659)

Co-authored-by: Hasan Ramezani <[email protected]>

Author: kschwab

pydantic_settings/sources/types.py

@@ -4,13 +4,13 @@
 
 from collections.abc import Sequence
 from pathlib import Path
-from typing import TYPE_CHECKING, Any, TypeVar, Union
+from typing import TYPE_CHECKING, Any, Union
 
 if TYPE_CHECKING:
     from pydantic._internal._dataclasses import PydanticDataclass
     from pydantic.main import BaseModel
 
-    PydanticModel = TypeVar('PydanticModel', bound=Union[PydanticDataclass, BaseModel])
+    PydanticModel = Union[PydanticDataclass, BaseModel]
 else:
     PydanticModel = Any