Give first footnote def priority over last

fuzz/src/lib.rs

@@ -812,7 +812,7 @@ pub fn normalize(events: Vec<Event<'_>>) -> Vec<Event<'_>> {
                     Event::Start(Tag::FootnoteDefinition(name)) => name.clone(),
                     _ => panic!("this should not be possible {footnote:?}", footnote = footnote),
                 };
-                footnotes.insert(name.to_string(), footnote);
+                footnotes.entry(name.to_string()).or_insert(footnote);
             }
 
             // Other events are passed through.