fix: bump check error

crates/xtask-bump-check/src/xtask.rs

@@ -333,9 +333,12 @@ fn changed<'r, 'ws>(
             (relative_pkg_root, pkg)
         })
         .collect::<Vec<_>>();
-    let base_tree = base_commit.as_object().peel_to_tree()?;
+    // Using a "symmetric difference" between base and head.
+    let ancestor_oid = repo.merge_base(base_commit.id(), head.id()).unwrap();
+    let ancestor_commit = repo.find_commit(ancestor_oid).unwrap();
+    let ancestor_base_tree = ancestor_commit.as_object().peel_to_tree()?;
     let head_tree = head.as_object().peel_to_tree()?;
-    let diff = repo.diff_tree_to_tree(Some(&base_tree), Some(&head_tree), Default::default())?;
+    let diff = repo.diff_tree_to_tree(Some(&ancestor_base_tree), Some(&head_tree), Default::default())?;
 
     let mut changed_members = HashMap::new();