Update talk next event date on cron

Run the `TalkDateUpater` service on each cron run to ensure that the
next event date for each talk is up to date.

Fixes #204

web/modules/custom/opd_talks/opd_talks.module

@@ -7,6 +7,16 @@
 
 declare(strict_types=1);
 
+use Drupal\opd_talks\Service\TalkDateUpdater;
+
+/**
+ * Implements hook_cron().
+ */
+function opd_talks_cron(): void {
+  $dateUpdater = Drupal::service(TalkDateUpdater::class);
+  $dateUpdater->__invoke();
+}
+
 /**
  * Implements hook_views_data_alter().
  */