fix(storage): let the S3 revalidation unique lock expire

RevalidateUnusableS3StoragesJob had no uniqueFor. A lock left by a
stopped worker blocked the job for up to 24 hours, so unusable S3
storages were not checked again and their backups were skipped.

- Set uniqueFor to 1800 seconds

tests/Feature/RevalidateUnusableS3StoragesJobUniqueLockTest.php

@@ -0,0 +1,25 @@
+<?php
+
+use App\Jobs\RevalidateUnusableS3StoragesJob;
+use Illuminate\Support\Facades\Queue;
+
+beforeEach(function () {
+    config()->set('cache.default', 'array');
+    Queue::fake();
+});
+
+it('does not queue a second revalidation while the unique lock is held', function () {
+    RevalidateUnusableS3StoragesJob::dispatch();
+    $this->travel(29)->minutes();
+    RevalidateUnusableS3StoragesJob::dispatch();
+
+    Queue::assertPushed(RevalidateUnusableS3StoragesJob::class, 1);
+});
+
+it('queues the revalidation again after a lock left by a killed worker expires', function () {
+    RevalidateUnusableS3StoragesJob::dispatch();
+    $this->travel(31)->minutes();
+    RevalidateUnusableS3StoragesJob::dispatch();
+
+    Queue::assertPushed(RevalidateUnusableS3StoragesJob::class, 2);
+});