All operators have an argument trigger_rule which can be set to 'all_done', which will trigger that task regardless of the failure or success of the previous task(s).
You could set the trigger rule for the task you want to run to 'all_done' instead of the default 'all_success'.
A simple bash operator task with that argument would look like:
task = BashOperator(
task_id="hello_world",
bash_command="echo Hello World!",
trigger_rule="all_done",
dag=dag
)