databases/pg_cron: Upgrade from 1.6.4 to 1.6.5

  Changelog:

    * Fix superuser check before adding job to CronJobHash
    * Fix leap year scheduling problem
    * Fix possible buffer underflow issue in cron parsing
    * Fix compilation warnings

  Taken from:

    https://github.com/citusdata/pg_cron/blob/main/CHANGELOG.md