Fix literal_string test on rustc older than 1.61

Author: dtolnay

tests/test.rs

@@ -115,10 +115,11 @@ fn literal_string() {
     assert_eq!(Literal::string("foo").to_string(), "\"foo\"");
     assert_eq!(Literal::string("\"").to_string(), "\"\\\"\"");
     assert_eq!(Literal::string("didn't").to_string(), "\"didn't\"");
-    assert_eq!(
-        Literal::string("a\00b\07c\08d\0e\0").to_string(),
-        "\"a\\x000b\\x007c\\08d\\0e\\0\"",
-    );
+
+    let repr = Literal::string("a\00b\07c\08d\0e\0").to_string();
+    if repr != "\"a\\x000b\\x007c\\u{0}8d\\u{0}e\\u{0}\"" {
+        assert_eq!(repr, "\"a\\x000b\\x007c\\08d\\0e\\0\"");
+    }
 }
 
 #[test]