test(logging): fix null formatter pyright error in setup test

Replace  check with  assertion to satisfy
pyright's handler-type compatibility check.

tests/test_logging_config.py

@@ -30,9 +30,11 @@ class TestConfigureLogging:
         assert len(root.handlers) == 1
         handler = root.handlers[0]
         formatter = handler.formatter
-        assert "%(name)s" in formatter._fmt
-        assert "%(levelname)s" in formatter._fmt
-        assert "%(asctime)s" in formatter._fmt
+        assert formatter is not None
+        fmt = formatter._fmt or ""
+        assert "%(name)s" in fmt
+        assert "%(levelname)s" in fmt
+        assert "%(asctime)s" in fmt
 
     def test_idempotent_second_call(self):
         self._clear_handlers()