Fix TypeError introduced in 2.5

Author: hramezani

pydantic_settings/sources.py

@@ -32,6 +32,7 @@
     Optional,
     Sequence,
     Tuple,
+    Type,
     TypeVar,
     Union,
     cast,
@@ -2115,7 +2116,7 @@ def read_env_file(
 def _annotation_is_complex(annotation: type[Any] | None, metadata: list[Any]) -> bool:
     # If the model is a root model, the root annotation should be used to
     # evaluate the complexity.
-    if isinstance(annotation, type) and issubclass(annotation, RootModel):
+    if annotation is not None and inspect.isclass(annotation) and issubclass(annotation, RootModel):
         # In some rare cases (see test_root_model_as_field),
         # the root attribute is not available. For these cases, python 3.8 and 3.9
         # return 'RootModelRootType'.