Event specified in timezone but `until` in UTC yields confusing error

[stefanv]

11:25:33 AM: RRULE UNTIL values must be specified in UTC when DTSTART is timezone-aware

Example cal:

name: Test
timezone: America/Los_Angeles
events:
  - summary: invalid RRULE event
    begin: 2026-01-13
    duration: { minutes: 60 }
    url: https://numfocus-org.zoom.us/j/86509289147?pwd=AXgP0r2sPYdekAyvenjbuztFbFwHvm.1
    repeat:
      interval:
        days: 7
      until: 2026-06-01 00:00:00 +00:00