test(xatu): use explicit path construction fixture

src/xatu/xatu_test.rs

@@ -14,7 +14,7 @@ fn source_file(path: &str, source: &str) -> SourceFile {
 fn future_sight_reports_clean_sources_as_clean() {
     let report = xatu::future_sight(vec![source_file(
         "clean.nix",
-        "{ value = builtins.toString x; inherit foo; }",
+        "{ path = ./. + \"/foo\"; inherit foo; }",
     )])
     .expect("fixture should parse");