allow null value for config option `delete_oldest_backups_when_using_…

…more_megabytes_than`

src/Config/StrategyConfig.php

@@ -12,7 +12,7 @@ protected function __construct(
         public int $keepWeeklyBackupsForWeeks,
         public int $keepMonthlyBackupsForMonths,
         public int $keepYearlyBackupsForYears,
-        public int $deleteOldestBackupsWhenUsingMoreMegabytesThan,
+        public ?int $deleteOldestBackupsWhenUsingMoreMegabytesThan,
     ) {}
 
     /** @param array<mixed> $data */