Compatibility with Zabbix < 6.4

[slls]

Hello, this seems like it might be able to upgrade the PagerDuty Zabbix integration from "might as well just use slack notifications instead" to actually very useful, so I mainly write here to thank you for publishing your efforts to make it such! It is pretty much exactly what I was looking for.
After couple of hours of figuring out why event updates made in PD would not propagate in my Zabbix 6.0 instance, even though the debug log of your script showed that the webhook was working and Zabbix API was responding to the script's requests with "null" without an error, same as if it was successful, copy pasting the Zabbix payload from the log into a curl command revealed that the requests were failing on authorization.
It seems that Zabbix only supports authorization in the request header since 6.4, earlier versions need an auth property with the token in the body of the request (6.4 supports either). I only needed to add one line to your script to make it work - auth => $zabbixtoken in the payload in the zabbix_event_update function, making it theoretically compatible with most previous versions of Zabbix. With that, it seems to be working very well. Thank you again!