fix UB in ffi tests

tests/scryer/helper.rs

@@ -54,7 +54,7 @@ pub(crate) fn load_module_test_with_tokio_runtime<T: Expectable>(file: &str, exp
 
 pub(crate) fn load_module_test_with_input<T: Expectable>(
     file: &str,
-    input: Cow<'static, str>,
+    input: impl Into<Cow<'static, str>>,
     expected: T,
 ) {
     use scryer_prolog::MachineBuilder;