fix: Correct non-string SDK key validation test

- Update test_validate_sdk_key_non_string to actually test non-string inputs
- Test various non-string types: int, None, object, list, dict
- Verify proper error message is logged for each invalid type

Co-Authored-By: jbailey@launchdarkly.com <accounts@sidewaysgravity.com>

Author: devin-ai-integration[bot]

ldclient/testing/impl/test_util.py

@@ -39,8 +39,13 @@ def test_validate_sdk_key_non_string():
     """Test validation of non-string SDK keys"""
     logger = Mock(spec=logging.Logger)
 
-    assert validate_sdk_key("123", logger) is True
-    logger.warning.assert_not_called()
+    non_string_values = [123, None, object(), [], {}]
+    
+    for value in non_string_values:
+        result = validate_sdk_key(value, logger)
+        assert result is False
+        logger.warning.assert_called_with("SDK key must be a string")
+        logger.reset_mock()
 
 
 def test_validate_sdk_key_empty():