parser: add a test for keep_tags(false)

Co-authored-by: Ethiraric <ethiraric@gmail.com>

parser/src/parser.rs

@@ -1126,5 +1126,9 @@ baz: "qux"
         assert_eq!(yaml["foo"].as_str(), Some("bar"));
         let yaml = &loader.documents()[1];
         assert_eq!(yaml["baz"].as_str(), Some("qux"));
+
+        let mut loader = YamlLoader::default()
+        let mut parser = Parser::new(text.chars()).keep_tags(false);
+        assert!(parser.load(&mut loader, true).is_err());
     }
 }