Create listing task with a default of 3 if unspecified

This will allow to retry task if they do not specify it.

swh/lister/core/lister_base.py

@@ -456,6 +456,7 @@ class ListerBase(abc.ABC):
                 if "priority" in self.config:
                     m["priority"] = self.config["priority"]
                 task_dict = self.task_dict(**m)
+                task_dict.setdefault("retries_left", 3)
                 tasks[_task_key(task_dict)] = (ir, m, task_dict)
 
         gen_tasks = (task_dicts for (_, _, task_dicts) in tasks.values())

swh/lister/launchpad/tests/test_lister.py

@@ -5,7 +5,6 @@
 
 
 def test_launchpad_lister(lister_launchpad, datadir):
-
     lister_launchpad.run()
 
     assert (
@@ -30,4 +29,4 @@ def test_launchpad_lister(lister_launchpad, datadir):
 
         assert row["policy"] == "recurring"
         assert row["priority"] is None
-        assert row["retries_left"] == 0
+        assert row["retries_left"] == 3