Add regression test

Author: JonathanBrouwer

tests/rustdoc-json/attrs/derive_helper.rs

@@ -0,0 +1,7 @@
+//@ is "$.index[?(@.name=='A')].attrs" '[{"other": "#[default]"}]'
+#[derive(Default)]
+pub enum Test {
+    #[default]
+    A,
+    B,
+}