Fix linting: correct import path in TYPE_CHECKING block

Changed `from tests.unit.sdk.conftest import BothClients` to `from .conftest import BothClients` to fix ruff import sorting error after merge from stable branch.

Co-authored-by: minitriga <[email protected]>

Author: Copilot

tests/unit/sdk/test_node.py

@@ -25,7 +25,7 @@
     from infrahub_sdk.client import InfrahubClient, InfrahubClientSync
     from infrahub_sdk.schema import GenericSchema, NodeSchemaAPI
 
-    from tests.unit.sdk.conftest import BothClients
+    from .conftest import BothClients
 
 # type: ignore[attr-defined]