fix: test code inconsistencies

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

Author: crepererum

guests/evil/src/fs.rs

@@ -111,7 +111,7 @@ impl String2Udf {
         Self {
             name,
             effect: Box::new(effect),
-            signature: Signature::uniform(1, vec![DataType::Utf8], Volatility::Immutable),
+            signature: Signature::uniform(2, vec![DataType::Utf8], Volatility::Immutable),
         }
     }
 }

host/tests/integration_tests/evil/env.rs

@@ -51,7 +51,7 @@ async fn call(udf: &WasmScalarUdf) -> Option<String> {
                 args: vec![],
                 arg_fields: vec![],
                 number_rows: 1,
-                return_field: Arc::new(Field::new("r", DataType::Null, true)),
+                return_field: Arc::new(Field::new("r", DataType::Utf8, true)),
             },
             &ConfigOptions::default(),
         )