Align DeliveryResult tags and make the index table test-local

Re-align the json tag column in DeliveryResult after the wider
DeliveryID gorm tag, and move the test's index table out of package
scope into the test function.

Model: opus-5-5

internal/database/event_tier_indexes_test.go

@@ -17,23 +17,23 @@ type indexedColumn struct {
 	field string
 }
 
-// eventTierIndexes are the columns the background work reads by: the
+// TestWebhookDBManager_OpenAddsEventTierIndexes verifies that opening a
-// recovery and sweep queries (status), the event log (event_id and
+// per-webhook database that predates these indexes creates them, so the
-// delivery_id) and retention (created_at).
+// queries that read by those columns stop scanning whole tables. It
-var eventTierIndexes = []indexedColumn{
+// stands in for an older database file by dropping the indexes
+// AutoMigrate just created, then reopening the same file.
+func TestWebhookDBManager_OpenAddsEventTierIndexes(t *testing.T) {
+	t.Parallel()
+
+	// The columns the background work reads by: the recovery and sweep
+	// queries (status), the event log (event_id and delivery_id) and
+	// retention (created_at).
+	eventTierIndexes := []indexedColumn{
 		{&database.Delivery{}, "Status"},
 		{&database.Delivery{}, "EventID"},
 		{&database.DeliveryResult{}, "DeliveryID"},
 		{&database.Event{}, "CreatedAt"},
-}
+	}
-
-// TestWebhookDBManager_OpenAddsEventTierIndexes verifies that opening a
-// per-webhook database that predates these indexes creates them, so the
-// queries above stop scanning whole tables. It stands in for an older
-// database file by dropping the indexes AutoMigrate just created, then
-// reopening the same file.
-func TestWebhookDBManager_OpenAddsEventTierIndexes(t *testing.T) {
-	t.Parallel()
 
 	mgr, lc := setupTestWebhookDBManager(t)
 	ctx := context.Background()