Add username setter.

classes/score.py

@@ -38,6 +38,16 @@ class Score:
         """
         return self._user
 
+    @user.setter
+    def user(self, username: str) -> None:
+        """
+        Setter for score's username.
+
+        Args:
+            username (str): username to set to
+        """
+        self._user = username
+
     @property
     def value(self) -> int:
         """