Fix clippy errors.

src/parser/babel_call.rs

@@ -244,7 +244,7 @@ mod tests {
         let input = OrgSource::new("()");
         let (remaining, call) = opt(babel_call_call)(input)?;
         assert_eq!(Into::<&str>::into(remaining), "()");
-        assert!(matches!(call, None));
+        assert!(call.is_none());
         Ok(())
     }
 }