fix: respect schedule flag in backup profiles

The `schedule` field in backup profile configuration was never checked
when registering backup jobs with the scheduler. This meant backups
would always run on schedule even when `schedule: false` was set.

Fixes #4039

system/src/Grav/Common/Backup/Backups.php

@@ -86,6 +86,10 @@ class Backups
         $inflector = $grav['inflector'];
 
         foreach (static::getBackupProfiles() as $id => $profile) {
+            if (!($profile['schedule'] ?? false)) {
+                continue;
+            }
+
             $at = $profile['schedule_at'];
             $name = $inflector::hyphenize($profile['name']);
             $logs = 'logs/backup-' . $name . '.out';