fix: use ISO format date strings in ical file as specified in https://datatracker.ietf.org/doc/html/rfc5545#section-3.3.5
fix: use ISO format date strings in ical file as specified in https://datatracker.ietf.org/doc/html/rfc5545#section-3.3.5

mortada/pelican-plugins,mortada/pelican-plugins,mortada/pelican-plugins,mortada/pelican-plugins,mortada/pelican-plugins