Fix clippy warnings in quiz3

This was already addressed by ceba18b476,
but only for the solution.

exercises/quizzes/quiz3.rs

@@ -23,7 +23,7 @@ impl ReportCard {
     fn print(&self) -> String {
         format!(
             "{} ({}) - achieved a grade of {}",
-            &self.student_name, &self.student_age, &self.grade,
+            self.student_name, self.student_age, self.grade,
         )
     }
 }