use /__api__/v1/timezones rather than /__api__/timezones (2024.09.0)

The Connect 2024.09.0 release publicizes the time zone enumeration API.

`connectapi::get_timezones()` needs to call this new endpoint when available and call the unversioned endpoint otherwise.

https://github.com/rstudio/connectapi/blob/bfefb00ce4721c0bb80aedf58ae217ff63742bee/R/schedule.R#L339-L345

The payload is unchanged; only the request path is different.