dead_code_tests: add skip multiple inherits test

src/dead_code_tests.rs

@@ -310,6 +310,17 @@ in alive
     assert_eq!(results[0].binding.name.to_string(), "dead2");
 }
 
+#[test]
+fn skip_multiple_inherits() {
+    let results = run("
+let
+  # deadnix: skip
+  inherit dead1 dead2;
+in alive
+    ");
+    assert_eq!(0, results.len());
+}
+
 #[test]
 fn shadowed_by_skip() {
     let nix = "