fix(calendar): use Calendars.Get for TZ lookup to fix SA 404

[markwatson]

Hi @steipete,

When using with a service account, I ran into some 404s when running: gog calendar list email@example.com (or events). This was true even when gog calendar calendars did in fact return a couple calendars.

It appears this is an issue with how service accounts manage their list of calendars. In time_helpers.go, we call CalendarList.get(calendarID):

 // getCalendarLocation fetches a calendar's timezone and returns it as a location.
func getCalendarLocation(ctx context.Context, svc *calendar.Service, calendarID string) (string, *time.Location, error) {
        //...

        cal, err := svc.CalendarList.Get(calendarID).Context(ctx).Do()
        //...

But svc.CalendarList doesn't contain the calendar for the service account, so it fails. Instead this change will use svc.Calendars.Get in order to always be able to lookup the calendars. I'm unsure what exactly controls this list for service accounts, but in my case I somehow had the calendars in the list, and then suddenly didn't. The documentation I found for the differences is here. There's also a similar change for the time zone helper.

I also manually retested this using the existing OAuth / standard flow documented in the README, and it appears to still
work. I would expect something similar to happen with the CalendarCalendarsCmd usage of svc.CalendarList.List(), but in my testing that did not seem to be the case.

Please let me know if I can change / improve any of this. I know it's a slight change, so if it's not something you want to do I won't mind. I needed the code for a project I was working on, so figured I would share it in case it's useful to others.

Thanks!

Mark

[markwatson]

Note: I accidentally opened this PR previously, but it wasn't tested enough. Now that I've tested it, I opened a new PR to keep the branch naming consistent (fix/...), instead of reopening the existing one. Apologies for the noise.

[markwatson]

These comments are probably unnecessary - I can remove them if needed.