Remove dispatch-failed age self-skip on Waterline dashboard test

Drops the markTestSkipped branch in
V2DashboardStatsControllerTest::testIndexExposesDispatchFailedAge.
The workflow rollout-safety contract pair
(operator_metrics.tasks.{oldest_dispatch_failed_at,max_dispatch_failed_age_ms})
ships in published workflow alpha 2.0.0-alpha.18, which Waterline's
composer install resolves for durable-workflow/workflow: ^2.0@dev.

Each key is now asserted unconditionally with assertArrayHasKey,
matching the matching-role / dispatch-overdue / run-wait / stuck-lease /
ready-due / claim-failed / retrying-activity removal pattern, so a
rename or drop of either fails CI loudly instead of silently
self-skipping.

Author: durable-workflow-ops

tests/Feature/V2DashboardStatsControllerTest.php

@@ -887,14 +887,9 @@ public function testIndexExposesDispatchFailedAge(): void
 
         $tasks = $response->json('operator_metrics.tasks');
 
-        if (! is_array($tasks)
-            || ! array_key_exists('max_dispatch_failed_age_ms', $tasks)
-            || ! array_key_exists('oldest_dispatch_failed_at', $tasks)) {
-            $this->markTestSkipped(
-                'Vendored workflow package predates the dispatch-failed age rollout-safety '
-                . 'contract (operator_metrics.tasks.{oldest_dispatch_failed_at,max_dispatch_failed_age_ms}).',
-            );
-        }
+        $this->assertIsArray($tasks);
+        $this->assertArrayHasKey('oldest_dispatch_failed_at', $tasks);
+        $this->assertArrayHasKey('max_dispatch_failed_age_ms', $tasks);
 
         $this->assertTrue(
             $tasks['oldest_dispatch_failed_at'] === null