Introduce latest_user_commits vs latest_commits

Author: woojiahao

src/git_autograder/branch.py

@@ -106,9 +106,13 @@ def user_commits(self) -> List[GitAutograderCommit]:
         return user_commits
 
     @property
-    def latest_commit(self) -> GitAutograderCommit:
+    def latest_user_commit(self) -> GitAutograderCommit:
         return self.user_commits[-1]
 
+    @property
+    def latest_commit(self) -> GitAutograderCommit:
+        return self.commits[-1]
+
     def has_non_empty_commits(self) -> bool:
         """Returns if a given branch has any non-empty commits."""
         for commit in self.user_commits: