Feature: Ephemeral action runners (#33570)

* This includes a runner mock test for hardend PickTask behavior like
described in my proposal
* Runner register ephemeral flag introduced in
https://gitea.com/gitea/act_runner/pulls/649

Closes #32461

models/migrations/migrations.go

@@ -375,6 +375,7 @@ func prepareMigrationTasks() []*migration {
 		newMigration(312, "Add DeleteBranchAfterMerge to AutoMerge", v1_24.AddDeleteBranchAfterMergeForAutoMerge),
 		newMigration(313, "Move PinOrder from issue table to a new table issue_pin", v1_24.MovePinOrderToTableIssuePin),
 		newMigration(314, "Update OwnerID as zero for repository level action tables", v1_24.UpdateOwnerIDOfRepoLevelActionsTables),
+		newMigration(315, "Add Ephemeral to ActionRunner", v1_24.AddEphemeralToActionRunner),
 	}
 	return preparedMigrations
 }