FIX: duplicate backrefs added on edit

.tsk/archive/tsk-25.tsk

···
+fix duplicate backrefs on edit
+

.tsk/next

···
-25
+26

.tsk/tasks/tsk-25.tsk

···
+../archive/tsk-25.tsk

Cargo.lock

···
 
 [[package]]
 name = "tsk"
-version = "0.2.2"
+version = "0.2.3"
 dependencies = [
  "clap",
  "clap_complete",

Cargo.toml

···
 [package]
 name = "tsk"
-version = "0.2.2"
+version = "0.2.3"
 edition = "2021"
 publish = true
 

src/workspace.rs

···
         let to_task = self.task(TaskIdentifier::Id(to))?;
         let (_, current_backlinks_text) =
             Self::read_xattr(&to_task.file, BACKREFXATTR.into()).unwrap_or_default();
-        let mut backlinks: Vec<Id> = current_backlinks_text
+        let mut backlinks: HashSet<Id> = current_backlinks_text
             .split(',')
             .filter_map(|s| Id::from_str(s).ok())
             .collect();
-        backlinks.push(from);
+        backlinks.insert(from);
         Self::set_xattr(
             &to_task.file,
             BACKREFXATTR.into(),