Set return type of tasks property to list[Task] instead of Sequence[T…

…ask]

PiperOrigin-RevId: 633363676

seqio/dataset_providers.py

@@ -1855,7 +1855,7 @@ def source_info(self) -> Optional[SourceInfo]:
     return self._source_info
 
   @property
-  def tasks(self) -> Sequence[Task]:
+  def tasks(self) -> list[Task]:
     sub_tasks = (mix.tasks for mix in self._sub_mixtures)
     return list(sorted(set(sum(sub_tasks, self._tasks)), key=lambda t: t.name))